
fkss I S 13,90 

Book JS^> 

Copyright^ 

CCEflUGHT DEPOSE 



RUBBER 
MANUFACTURE 



THE CULTIVATION, CHEMISTRY, TESTING, AND 
MANUFACTURE OF RUBBER, WITH SECTIONS 
ON RECLAMATION OF RUBBER AND THE 
MANUFACTURE OF RUBBER SUBSTITUTES 



By 

H. E. SIMMONS 

Professor of Chemistry, Municipal University of Akron, Ohii 



ILLUSTRATED 



NEW YORK 

D. VAN NOSTRAND COMPANY 

EIGHT WARREN STREET 
1921 









- 



Copyright. 1921 
by 
D. Tax Nostrastd Company 









^\ 



Printed in the United States of America 



©CU611344 

m 2B 1921 



TO 

M Y PARENTS 

who by their sacrifices made it 

possible for me to obtain 

an education. 



PREFACE 

The author has attempted to give in this volume a brief but com- 
plet»survev of the Rubber Industry. The production of crude rub- 
ber, including the methods in use for collecting both wild and plan- 
tation rubber, are carefully described as well as the processes in use 
for coagulating and curing the crude rubber. 

The manufacture of numerous inorganic fillers and their proper 
use in rubber compounding are given in full as well as the various 
processes employed for fabricating rubber goods. The apparatus 
used in all parts of the industry is fully illustrated and described. 

The chemical and physical properties of the latex and rubber, 
including the production of synthetic caoutchouc, are fully discussed. 
Chapters have also been included on the chemical analysis and phys- 
ical testing of rubber and its compounds and the various theories of 
vulcanization. 

While the attempt has been made to present the technical fea- 
tures of the subject in a scientific manner so that the volume will be 
of value to students of this subject, it is believed that a large part of 
the volume will be of interest to the non-technical reader. Both 
classes of readers will no doubt be interested in the attempts to point 
the way for the future development of this most important product. 

H. E. S. 

Akron. Ohio. 

Februarv 1. 1921. 



CONTENTS 



CHAPTER I 
THE HISTORY OF CAOUTCHOUC ' 1 

CHAPTER II 

RUBBER OF THE AMAZON BASIN 4 

Varieties. Methods of Tapping. Coagulating Latex. 

CHAPTER III 

AFRICAN RUBBERS. INCLUDING THOSE FROM MADAGASCAR. 11 
A'arieties. Coagulation. Obtaining and Coagulating Latex from Tines. 

CHAPTER IV 
CENTRAL AMERICAN RUBBERS IS 

CHAPTER V 

RUBBER PLANTATIONS AND THEIR DEVELOPMENT 26 

Ceylon. Malaya. Planting Rubber Trees. Cultivating the Land. Tapping tbe 
Trees. Coagulating the Latex. Tree Diseases and Other Pests. Other Varieties of Rub- 
ber Trees. 

CHAPTER VI 

DISCUSSION OF COLLOIDS 37 

Brownian Movements. Characteristics of Sols. Surface Tension. Cataphoresis and 
L lectro-endosmos. 

CHAPTER VII 

COLLOIDAL ACTION OF CRUDE RUBBER AND ITS APPLICA- 
TION IN RUBBER MANUFACTURE 43 

Preservation of Latex. Coagulation by Chemicals. Application of Colloidal Chem- 
istry. 

CHAPTER Mil 
DIFFERENT MEANS OF COAGULATION 17 

CHAPTER IX 
THEORY OF THE CONSTITUTION OF RUBBER 55 

CHAPTER X 
SYNTHETIC CAOUTCHOUC 59 

CHAPTER XI 

CHEMICAL AND PHYSICAL TESTING OF CRUDE RUBBER 64 

Washing Loss. Determination of Moisture. Estimation of Resin. Determination of 
Ash. Itetermination of Nitrogen. Determination of Insoluble Matter. Determination of 
Rubber. Viscosity of Rubber. Specific Gravity. Sun Cracking. Vulcanizing Test. 



CHAPTER XII 

THE MANUFACTURE AND USE OF INORGANIC FILLERS 71 

Inorganic Accelerators. Barytes. Aluminum Compounds. ' Talc. Silicon Oxides. 
Asbestos. Calcium Carbonates. Sulphides. Magnesium Carbonate. White Pigment. Zinc 
Oxide. Zinc Sulphides. Lithopone. Barytes and Kaolin. Bed Pigments. Golden and 
Crimson Antimony. Iron Sesquioxide. Bouge.' Bed Ochre. Bed Hematite. Vermilion. 
Black Pigments. Lampblack. Bone Black. Gas Carbon. Black Hypo. Graphite. Lead 
Sulphide. Yellow Pigments. Yellow Ochre. Chrome Yellow. Cadmium Yellow. Arsenic 
Trisulphide. Yellow Dyestuffs Used. Green and Blue Pigments. Chrome Green. Bin- 
mann's Green. Ultramarines. Prussian Blue. Thenard's Blue. 

CHAPTER XIII ; 

THE MANUFACTURE AND USE OF ORGANIC ACCELERATORS. . 85 
Action of Catalysis. Accelerators. 

CHAPTER XIV 

THE MANUFACTURE AND USE OF RUBBER SUBSTITUTES 92 

CHAPTER XV 

THEORIES OF VULCANIZATION 98 

Weber's Theory. Oswald's Theory. Spence's Experiment. Reversibility of Vulcani- 
zation Process. Migration of Sulphur in Rubber. Researches by Loewen. Vulcanization 
and Viscosity. Ostromislensky's Theory. 

CHAPTER XVI 

METHODS OF RECLAIMING RUBBER 105 

Devulcanization Processes. 

CHAPTER XVII 

PREPARATION OF CRUDE RUBBER FOR MANUFACTURING Ill 

The Receiving Boom. Washing. Drying. Mixing Mills. 

CHAPTER XVIII 

THE PRINCIPLES OF COMPOUNDING 117 

Tensile Strength. Elasticity. Ageing Qualities. Colors. Specific Gravity. Scorching. 

CHAPTER XIX 

CHEMICAL ANALYSIS OF MANUFACTURED RUBBER 123 

Procedure of Analysis. Determination of Organic Content. Determination of Sul- 
phur. Barium Sulphate Troubles. Determination of Mineral Oil. A'aseline and Paraffin. 
Determination of Rubber Substitute. Determination of Rubber Content. Determination 
of Sulphur. Analysis of Mineral Matter. Determination of Carbon or Graphite. 

CHAPTER XX 

PHYSICAL TESTING OF COMPOUND SAMPLES 132 

Tensile Strength. " Grain." Hardness. Hysteresis. Specific Gravity. Artificial Age- 
ing Tests. Light Tests. Weather Exposure Tests. Dielectric Tests. Viscosity Tests. 
Friction Tests. Barbeque Test. 

APPENDIX 

THE LABORATORIES AND EQUIPMENT OF THE MUNICIPAL 

UNIVERSITY OF AKRON 147 

The Bubber Laboratory Equipment. Brief Description of the Course. Two Industrial 
Fellowships. r , 



CHAPTER I 
The History of Caoutchouc 



Before starting this series of chap- 
ters, it seems to me both necessary 
and interesting to take a brief glance 
into history and obtain a little knowl- 
edge as to when and by whom this 
important article of commerce was 
first found. It is my purpose to 
deal principally with the rubber 
industry as it is at the present time, 
yet to omit mentioning the discovery 
of this substance would be unfair 
to the pioneers, and would also render 
a work of this nature incomplete. 

It has been stated that the first 
reference to rubber occurs in the 
work of a Spanish writer of Madrid 
in 1536, but M. L. Tillier points out 
that P. Martyr d'Angliera in 1525 
published a description of some rub- 
ber playing balls seen by him. in 
Mexico. 

Another Spanish writer describes 
the same article as made " from a 
black resin, obtained from a tree 
called by the natives Ulaquhuil. " In 
this connection it will be well to state 
that in parts of Mexico and Central 
America even to-day the Castilloa 
elastica is known as the Ule tree. 

According to Morris, the first 
record of india-rubber was made soon 
after the discovery of the New World 
by Columbus. The Old World rub- 
bers were still unknown. Columbus, 
on his second voyage, noticed the 
inhabitants of Hayti playing with a 
ball made from the resin of a tree. 
It is interesting to note that the game 
which the natives played with these 
balls is still played in these regions 
and in fact, modern explorers have 
become aware of the presence of rub- 
ber yielding trees simply by observ- 
ing that this game was being played. 
Antonio de Herrera Tordesillas, a 
Spanish historian in 1601, in his 
" General History of the Voyages 



and Conquests of the Castillians 
while speaking of the conquests in 
Mexico, mentions certain trees which, 
when punctured, yield a milk which 
becomes converted into a gum with 
a very fine smell. 

Father Xavier de Charleroix of 
the Society of Jesus, 1682-1761, de- 
scribes the Batoa, a species of ball 
of a solid matter but extremely 
" porous and light. It soars higher 
than other balls, falls to the ground 
and rebounds higher than the level 
of the hand which it quitted. It falls 
to the ground and rebounds once 
more although not to such a height 
this time, and the height of the bound 
is gradually diminished." 

Whatever the date may be which 
marks the first recognition of this 
important article in civilization, we 
at least must give credit to the Span- 
ish and Portuguese explorers of the 
West Indias as being the first to ob- 
serve it and record it in their litera- 
ture. 

The French were the first to make 
any scientific study of rubber bear- 
ing plants. The Academy of Science 
of Paris in 1731 sent an expedition 
to South America under the guidance 
of La Condamine and Bougner. In 
1736, La Condamine sent back to the 
Academy a resinous mass under the 
name of " caoutchouc " and this 
information : 

" There grows in the province of Bs- 
meraldas, a tree called by the natives of 
the country ' Heve ' ; there flows from it, 
by simple incision, a liquor, which 
hardens gradually and blackens in the 
air. The inhabitants make flambeaux of 
it, which burns very well without wicks, 
and gives rather of a fine light. . . . 
In the province of Quito, sheets of linen 
are coated with it. and are used for the 
same purpose as we use waxcloth. . . . 
The same tree grows along the banks of 
the Amazon and the Mainas Indians call 



RUBBER MANUFACTURE 



the resin which they extract from it 
' cahuehu ' ( pronounce caoutchouc ) . They 
make hoots of it, which do not draw 
water, which after being blackened by 
being held in the smoke, have all the ap- 
pearance of leather. They coat earthen 
molds in the shape of a bottle with it, 
and when the resin has hardened, they 
break the mold and force out the pieces 
through the neck and mouth ; thus they 
get a nonfragile bottle, capable of con- 
taining all kinds of liquid." 

He also mentions a peculiar use 
which one of the tribes made of 
this india-rubber : 

" The use which is made of this resin 
by the Omaguas, in the middle of the 
American continent, on the banks of the 
Amazon, is still more singular ; they 
make bottles of it in the shape of a pear, 
to the neck of which they attach a fluted 
piece of wood. By pressing the bottles 
the liquid which they contain is made to 
flow out through the fluted piece of wood, 
and by this means these bottles become 
real syringes." 

That is the origin of the name 
given by the Portuguese to the tree 
which yields this resin, Pao de 
Ciringa (syringe-wood), and of ser- 
ingueiros to the resin collectors. 

At this point La Condamine had 
to give up his pursuit of this peculiar 
substance and devote his time to his 
own profession, for he was a doctor 
of medicine' and an eminent natur- 
alist. At this time he came in touch 
with Fresneau. the French engineer 
located at Cayenne, who seemed to 
grasp the importance of this sub- 
stance and took up the work where 
La Condamine had abandoned it. 
After great labor and hardship he 
succeeded in finding these trees and 
noticing how the natives proceeded 
to obtain this resin, he sent the fol- 
lowing communication to La Con- 
damine : 

" They commence by washing the foot 
of the tree ; then they make with a bill- 
hook, longitudinal but rather oblique 
incisions which should penetrate the 
whole thickness of the bark, taking care 
to make them, one above another, so that 
the flow from the top incision falls into 
the one underneath, and so on until the 
last one at the bottom of which a leaf 
of the Balizier (an American reed) is 
placed, which is made to hold the liquid 
by potter's earth, so as to lead the juice 
into a vessel placed at the foot of the 
tree. 

"To utilize the milky juice of the trees 
which I ha^e" mentioned, a mold is made 
of potter's earth, according to the shape 
of the vessel which it is intended to make, 



and, to hold it more conveniently, a. 
piece of stick is inserted in the place 
which is not to be coated with the milky 
juice. An aperture is thus secured 
through which the potter's earth may be 
afterward expelled, by introducing water 
to soften it. Any one mold being shaped, 
polished, and softened with water, it is 
coated all over with milky juice by means 
of the fingers, after which this coating 
is exposed to a dense smoke, where the 
heat of the fire hardly makes itself felt, 
keeping constantly turning it. so that the 
juice may be spread equally over the 
mold, and taking good care that the flame 
does not reach it, which would cause the 
milky juice to boil, and thus to form 
small holes: 

" As soon as a yellow color is seen, 
and this first coating is no longer tacky 
to the fingers, a second layer is applied, 
which is treated in the same way, and 
so on with the other coats, until it is 
judged to be sufficiently thick, and then 
it is kept longer over the flame so as 
to evaporate the whole of the moisture, 
until but the elastic resin remains. . . . 
With this juice and linen sheeting, tar- 
paulins, pump hose, divers' clothing, bot- 
tles, sacks for containing campaigning 
biscuit, etc., may be made, without fear 
of this material imparting any bad smell ; 
but all of these things can only be exe- 
cuted on the spots where the tree grows, 
as these juices soon lose their fluidity." 

In 1762 the French botanist Fuset- 
Ablet started for Guiana and two 
years later he published " The Flora 
of Guiana," and in this he described 
a tree which he called Hevca Guyan- 
cnsis. 

In 1798 James Howison determined 
the name of an elastic gum vine, the 
species which later on was called 
Urceola elastica. This tree was the 
chief source of supply from the East 
prior to the introduction of that from 
the Fie us elastica. It was discovered 
on the island of Penang. While 
clearing a way through the jungle 
with cutlasses, the blades became 
covered with a juice which hardened 
aud had the appearance of india-rub- 
ber. The source of this juice was 
found to be a vine about as thick 
as a man's arm, which ran along the 
ground for great distances, rooted 
at its joints and also climbed the 
highest trees. It was thought to be 
a species of Hevea, with which it is 
often confused even to this clay. This 
juice w-as also used by the natives 
to waterproof different articles. 

It is reported that in 1755 the King 
of Portugal, having heard of the 



THE HISTORY OF CAOUTCHOUC 



waterproofing material of the In- 
dians, sent several pairs of his royal 
boots to Para in order that they 
might be covered with rubber. 

Priestley is credited with having 
given this substance the recommenda- 
tion to use for effacing pencil marks, 
and from this it was called " india- 
rubber. ' ' 

W. H. Johnson gives us the deriva- 
tion of the word caoutchouc as com-~i 
ing from caucho, which in turn comes 
from cao, meaning wood, and o-chu, 
meaning to run or weep. 



In this work I shall use the term 
" caoutchouc " when reference is 
made to the pure hydrocarbon while 
I shall use india-rubber as a term for 
the crude product whether raw or 
manufactured. 

When we realize that it was toward 
the end of the eighteenth century 
before rubber was introduced into 
Great Britain the wonderful advance 
made in this length of time makes it 
impossible for us to prophesy what 
the future has in store along this line. 



CHAPTER II 
Rubber of the Amazon Basin 



As stated in Chapter I. the French 
were the pioneers in obtaining exact 
information in regard to the South 
America rubbers. It was the expedi- 
tion of de La Condamine and Boug- 
ner. from the Paris Academy of 
Science, in 1731. that sent the first 
reports dealing with rubber in Peru 
and Brazil back to the Eastern World. 

In 1736 de La Condamine sent 
home samples of rubber, and referred 
to the fact that in the province of the 
Esmeraldas there occurred a tree 
called by the natives Hevea, and that 
they obtained from it a milk white 
liquid, which gradually hardened and 
blackened in the air. He also men- 
tioned that in the province of Quito 
the natives coated linen with this ma- 
terial, and that the same tree grew 
on the banks of the Amazon : also 
that the natives made water tight 
boots from it, which had the real ap- 
pearance of leather, after having 
been blackened by means of smoke, 
lie goes further and says that the na- 
tives made some moulded goods from 
this material. From his writings we 
find several of the terms still in use. 

I mention this simply to give some 
idea as to the length of time civ- 
ilized man has been acquainted with 
this important substance, and in what 
condition and state of development 
he found it. 

In the beginning it is well to de- 
fine a few of the terms which will be 
used and describe briefly the labor 
condition which prevails throughout 
nearly all of the South America rub- 
ber regions. 

Thus far very little of the vast ter- 
ritory bearing these rubber produc- 
ing trees has been even explored, to 
say nothing of their being available 
for tapping. I*' is estimated that there 



are at present 300.000.000 virgin 
trees in this territory. 

Tracts of this rubber producing 
region are obtained by individuals or 
companies on lease from the state, 
and the working of any area which 
has not been surveved by the state is 




Fig. 1 

punishable under the law of theft. 
The number of leases and sub-leases 
is considerable. From the report of 
the Commission of Economic Expan- 
sion in Brazil during the year 1906- 
07 there were organized fifty-two 
such companies with a capital of two 
millions sterling. These concessions 
are termed scringals, and are usually 
computed according to the number 
of estradas running through them. 
The estradas are paths running 



RUBBER OF THE AMAZON BASIN 



through the forest in such a way as 
to lead past from one hundred to one 
hundred and fifty trees. Sometimes 
the trees are some distance apart, but 
generally they are found in groups of 
from two to six. 

The seringueiro is the name applied 
to the one taking care of a scringed. 
The seringueiros are mostly natives of 
the states of Ceara and Maranhao. 
Due to the high death rate and the 
great number of desertions, it is nec- 
essary to provide about eighty labor- 
ers for a scringal on which fifty could 
actually do the work. One serin- 
gueiro is supposed to take care of two 
estradas after they are opened up and 
[tut into operation. 

The cost of financing a scringal is 
rather high, as Sandmann has esti- 
mated it costs about $25,000 to put 
into operation a scringal of one hun- 
dred estradas, that is, from 10,000 to 
15,000 trees. This will buy the outfit 
necessary, cut the paths, build the 
huts and factory, and also allow for 
a little incidental expense. 

The patrao, the owner or sub-owner 
of a seringal, veiy seldom finances his 
own property. He obtains the ad- 
vances from the large dealers and ex- 
port firms at Para and Manaos. They 
are termed aviadorcs. Thus it will be 
seen that the financing is really done 
by the aviadores, and they hold a 
mortgage on the patrao, who in turn 
mortgages the labor of the serin- 
gueiro. 

The average yield of a six months' 



season of an industrious seringueiro 
is about eight hundred pounds of 
rubber. When he has paid his ad- 
vances to the patrao there remains a 
profit of about $250 to $300. This is 
hardly sufficient to support his fam- 
ily at the seat of operations during 
his absence on the seringal. It is for- 
tunate for him that the streams and 
forest furnish fishing and hunting al- 
most sufficient to support him, but 
because of the poor way in which the 
food is prepared and the unhealthy 
climatic conditions, there is much 
sickness and the mortality is high. 
The occupation of a seringueiro is not 
an enviable one. 

Varieties 

In the Amazon Basin we find the 
order of Euplwrbiaceae, the most im- 
portant genus of which is the Hevea, 
and here we find many different 
species, the most important one be- 
ing the Hevea orasiliensis, the species 
from which the widely known Pai'a 
rubber is obtained. This species is 
found over a large part of northern 
South America but principally in the 
areas watered by the Amazon and its 
tributaries, in the states of Para, 
and Amazonas, in Brazil. This is the 
species from which the Eastern plan- 
tations have been largely propagated. 
It is a large tree, in its natural state 
often attaining a height of one hun- 
dred feet and a diameter of forty 
inches. 

There are several varieties obtained 
from the Hevea brasiliensis. 



>> 
1 


W^^k * " It «P.I»I ' ■llTfaii f'lll 1 S'^IL' 

'Ma' ?»''? '5*T L jL||]j' 



Fig. 2 — Rubber Gatherers Dressed for a Holiday 



RUBBER MANUFACTURE 



We find two main regions in which 
Fine Para is prepared, the ' ' Islands ' ' 
at the mouth of the Amazon River; 
and the " Up-river " regions near 
and above Manaos. " Islands " rub- 
ber is generally known as " soft- 
cure," and " Up-river " as " hard- 
cure." 

The scraps of rubber adhering to 
the bark of the trees and coagulating 



SiijJlPb'' '--- -ill '*' I 










% 


|S®l-'i- ; -'-2 










9 


■ft^s!! 




wm, ' ! ""?^ i i 




Hvr'x 




Em&teib.3at 







Fig. 3 — Tapping Wild Rubber Trees 

cups are compressed into irregular 
forms and sold as " Negroheads." 
" Up-river Negroheads " are gener- 
ally called" scrappy "and" Islands 
Negroheads " are called " Sernam- 
by. " There is another variety of 
negrohead, the Cameta, coming from 
a district of that name in Southwest 
Para. 

This same species supplies from the 
Province of Matto-Grosso, in Brazil : 
the Matto-Grosso, Fine and Entre- 
fine ; Matto-Grosso, Virgin Sheets, 
and Matto-Grosso, Negroheads. 

From Bolivia we obtain Bolivian, 
fine, medium and coarse ; also Mol- 
lendo, fine, medium and coarse. These 
are also obtained from a species of 
Hevea. 

From Petri we get Peruvian (fine. 



coarse or scrappy), likewise of the 
Hevea. 

From Ecuador we obtain a new 
species, the Sapium, several varie- 
ties of which are : Ecuador scrap, 
sausage ; Esmeralda sausage, Caucho 
bianco, and Caucho negro. 

Confused with these last two we 
often come in contact with a variety 
known as Caucho Balls which is of 
the Hevea brasilicnsis. 

During the last quarter of a cen- 
tury large quantities of Caucho have 
been found in the districts of Obidos, 
Tocantins, Xingo, and Tapajos rivers. 
This supply is likely to be exhausted 
due to the fact that the natives gather 
this latex by cutting down the tree 
and then bleeding it. 

There are some seventy varieties of 
the Manihot rubber but we shall call 
attention to but two, the Ceara and 
Manicoba which grow in a relatively 
poor soil and at altitudes where most 
other rubber producing trees cease to 
exist. The bulk of these rubbers come 
from the Province of Ceara, Brazil. 
There is some difficulty in collecting 
this latex due to its rapid coagulation. 

The natives allow the latex to 
coagulate as it flows down the tree 
and then peel it from the bark. It 
sometimes runs down onto the ground 
and is caught in a leaf formed as a 
receptacle. The result is that the 
Manicoba rubber varies a great deal 
and contains a large amount of for- 
eign matter. When this rubber is 
properly prepared, however, it is of 
a very good grade. 

The Micandras occurs on the upper 
Amazon and some are of the opinion 
that it is used largely in the making 
of Scrappy Negroheads. 

A rubber of the species Hancornia 
is also found in Brazil and is sold 
under the name of Matto-Grosso 
Sheets, Mangabeira, or Pernambuco. 
It is of medium value and rather 
large quantities of it are used. 

The above enumeration does not 
include all of the varieties of rubber 
from South America but it does cover 
the most important ones. 

Tivo Methods of Tapping 

All of the South American rubber 
comes from trees and is obtained by a 



RUBBER OF THE AMAZON BASIN 



system of tapping of one kind or 
other. We shall consider two general 
methods. 

1. Felling of trees. 

2. Bleeding by puncture or inci- 
sion, tapping. 

By the felling process it is possible 
to obtain only the latex which is in 
the tr.ee at the time of its cutting. 
The method is a destructive one and 
is only practiced now under two con- 
ditions. 

The trees found in Peru, when once 
tapped are attacked by insects and 
the death of the tree results, while if 
tins tree is cut down there springs up 



er the incision was too deep and thus 
impaired the life of the tree, and got 
injurious material into the latex, or 
too shallow and thus obtained a poor 
yield of latex. 

From these incisions the latex flows 
down the tree until it comes to the 
rope and then on down the groove 
which the tree forms with the rope 
until it reaches the lowest point where 
it is collected in a suitable receptacle. 
The latex making this journey down 
the tree collects' moss, wooden debris 
and other impurities and these are all 




-Smoking Caoutchouc 



from its stump several sprouts which 
grow very rapidly and in a short time 
a clump of trees exists where there 
was but one originally. In the sec- 
ond place felling is allowed where it 
is necessary to thin out the forests in 
order to make the estradas. 

Several different methods of tap- 
ping are in use. The Arroclio 
system was one of the first to be 
used in Brazil, and was accomplished 
by binding a rope obliquely about the 
Hevea, the knot being high up on the 
tree. Above the ligature, incisions 
were made with any sort of tool the 
operator happened to have, a butch- 
er's knife, pruning hook, or cutlass, 
and the seringueiro cared little wheth- 



Fig. 5 — Native Collecting the Latex 



later found in the rubber. In addi- 
tion to getting poor rubber the serin- 
gueiro would often neglect to remove 
the rope and the tree would die of 
strangulation. This process has been 
practically abandoned. 

The present method of tapping in 
this region has been described by a 
great many different writers. Chapel 
and Carrey have probably given the 
best description. The "seringueiro 
gets his outfit all together which con- 
sists of a machaclo, a small hatchet 
with a short handle and a blade 
only 3 centimeters wide with a 
sharp cutting edge of about 5 centi- 
meters, the bucket for carrying the 
latex, and the tigelinhas, small cups 



RUBBER MANUFACTURE 



which are hung at the different in- 
cisions. 

With this equipment the serin- 
gueiro starts out about five o "clock iu 
the morning to operate on his es- 
trada, which begins at his hut and 
after its ramifications leads back to his 
hut again. He takes with him his ma- 
chado and tigelinhas. When he comes 
to a tree he cleans away the rubbish 
at its foot, cleans the bark, and then 
begins to tap the tree. With a 
single cut of the machado he incises 
the bark, so that the latex flows out. 
being careful not to wound the tree. 
After several incisions of this kind 
have been made in each tree, he places 
a tigelinhas under each one to collect 
the latex and then moves on and 
repeats the operation on the next tree. 

Some of the collectors make V- 
shaped incisions and others make ver- 
tical ones. Whichever method is used 
should be practiced regularly on the 
tree for it has been found that by 
using irregular tappings the tree will 
yield regularly only for a year or two 
and will then dry up and cease to 
give any latex. 

A seringa tiro is able to operate 
about fifty trees a day so if his 
estrada contains one hundred and 
fifty trees he divides it in such a way 
that each tree is tapped every third 
day. If his estrada contains one hun- 
dred, then each tree is tapped every 
other day. After he has tapped his 
fifty trees lie comes into his hut for a 
little rest and a cup of coffee. 

This has consumed about three hours 
and he now takes up his baldc. or tin 
bucket, and revisits the trees which 
he has tapped, pouring the latex from 
each tigelinhas into his gathering 
bucket and turning the tigelinhas up- 
side down on a stick near the foot of 
the tree. This is done to prevent its 
being filled with water and collecting 
impurities, as it rains every day dur- 
ing this season of the year. 

The period of collecting latex is 
from the later part of August to the 
first of January. After all of the 
latex is gathered he returns to his hut 
and the remainder of the day is spent 
preparing the rubber from -this run. 

Latex is the liquid containing the 



rubber which exudes from the tree, 
but is not the sap of the tree. It may 
be thought of as analogous to the milk 
of mammals, which i't is often called. 
the rubber corresponding to the but- 
ter fat. and of course must be sep- 
arated out. The process of obtaining 
the rubber from the latex is called 
coagulation. 

Coagulating Latex 

The workman starts a fire in his 
fumiero, a kind of furnace sur- 
mounted by a short conical pipe 
which will deliver the fumes so that 
they do not spread too far afield. He 
then tills his fumiero with the fuel 
which has been carefully selected and 
ignites it. The best fuel for this pur- 
pose is the nuts of the urucuri. Some 
wood is mixed with these to keep 
them burning, and also to conserve 
the supply. 

As soon as the smoke is given off 
abundantly the cauchero takes a 
paddle and holds this in the smoke 
from his fumiero until it is covered 
with a layer of carbon. This is done 
to prevent the rubber from sticking 
to it. He then dips the paddle into 
the latex at his side, allows it to drain, 
then holds it in the dense smoke until 
it assumes a yellow tinge. 

The rubber is coagulated almost 
immediately and the mother liquor 
exudes and is evaporated by the heat 
of the fumiero. When this is done, 
the first layer is complete and he 
again dips the paddle into the latex 
and repeats the same process, thus 
building up a biscuit of rubber with 
one thin layer upon another and each 
one coagulated separately. 

When this biscuit has attained a 
weight of ten or eleven pounds he 
frees it from the paddle by cutting it 
down in the direction of its axis and 
is now ready to begin over. These 
biscuits are still moist and to dry 
them, he places them in the sun for 
several days. They are then ready 
for the market under the name of 
Para Fine. The size and shape of 
these biscuits varies considerably in 
accordance with the way they are 
made. 

The cauchero often takes a pole 
about seven feet long and supports 



RUBBER OF THE AMAZON BASIN 




moking Rubber 



this over his fire by placing one end 
in a loop suspended from the roof of 
his hut and holds the other end in his 
left hand, with which he keeps it 
turning continually, while with the 
other hand he pours a small amount 
of latex over the pole which is in the 
smoke. By this method the same 
grade of rubber is produced but in 
larger biscuits, averaging about forty 
or fifty pounds. This is the method 
of coagulating the latex of all of the 
Paras, and it is undoubtedly the vir- 
tues of this process which has given 
the Para its enviable position- in the 
rubber trade. 

There are two reasons at least for 
the excellence of this rubber ; first, the 
smoke has a large amount of carbon in 
it and Ave know this substance pos- 
sesses energetic antiseptic properties; 
second, in the products of distillation 
of the uricuri nuts there is a consider- 
able amount of creosote which also 
possesses the same property. There- 
fore we have a double protection 
against fermentation and decomposi- 
tion of the nitrogenous matter pi'esent 
in rubber coagulated by this method. 

The ilanihot latex is coagulated by 
natural heat. As was stated before, 
the seringueiro obtains the Ceara and 
Manicoba by tapping the tree with 
long gashes as high up on the tree as 



he can reach. The latex is very thick 
and coagulates 
before it ever 
comes t o t h e 
ground. H e 
allows it to re- 
main two o r 
three days or 
until it is dry, 
w hen he de- 
taches it a n d 
either rolls it 
up into a ball 
o r folds i t 
back and forth 
upon itself. 
Without fur- 
ther treatment 
it comes into 
the market as 
Ceara Scraps. 
There are 
three grades 
of this rub- 
ber ; the first 
quality is a 
blonde rubber 




Fig. 7 — Ball of Rub- 
ber After Smoking 



which is collected at the beginning 
of the season ; the second quality is 
darker in color, and is collected 
later on when the rains have begun 
to fall; the third quality is that 
which is collected at the foot of the 
trees and is full of earthy mate- 
rial, often as much as 50 per cent. 



10 



RUBBER MANUFACTURE 



This rubber always gives off: a 
strong smell due to the careless treat- 
ment in its collection. Naturally this 
is a higher grade latex than that from 
the Hevca, and it is a pity that more 
care is not exercised in its prepara- 
tion. 

A chemical means of coagulation 
was proposed by Strauss for use with 
the Hancomia latex. It consists in 
pouring into the latex a solution of 
potassium alum when coagulation 
takes place immediately. The rubber 
is then allowed to drain for about 
eight days, then divided into small 
pieces and sun-dried for a month 
when it is ready for market. 

Due to the rapid coagulation, we 
find enclosed latex all through rubber 
made by this process which not only 
constitutes loss but which further fer- 
ments and produces a bad odor; we 
also find pockets filled with the alum 
solution which has a very injurious 
effect upon the rubber. As a result 
this rubber deteriorates with age, and 
it often has a loss of as high as 60 per 
cent. There are three grades of Man- 
gabeira, and the one possessing a 
red color sells at a premium. 

This alum process has been dis- 
placed in certain regions by sulphuric 
acid, but this does not remedy the 
objections already mentioned, and of 
course it has no antiseptic property. 
To correct this, a solution of common 
salt has been used but it leaves too 
large a quantity of water in the rub- 
ber. A soap solution has been used 
but this, in addition to having the 
same objections, acts very slowly. 

The juices of some plants and 
climbers have also been employed, but 
the difficulty of obtaining these and 
the fact that they introduce more 
resins into the rubber has resulted in 
their condemnation. 

The above comprise the more im- 
portant methods of coagulation which 
are in use or have been used in South 
America, the best one being the 
smoking, and it is worthy of mention 
in this connection that this is the 
method which de La Condamine 
found the natives usin°: in 1731. 



One thing which consumers of rub- 
ber are very anxious to have is uni- 
formity, and there are several factors 
which tend to produce a poor prod- 
uct : 

First, if the trees have been im- 
properly tapped, that is if the 
seringueiro has cut too deeply and 
pierced the cambium, some of the sap 
of the tree will enter the latex and 
impair the rubber, making it tacky ; 

Second, when in gathering the 
latex of one species is mixed with 
that of another or even with that of 
a tree that is too young ; 

Third, carelessness in gathering 
and coagulating. The most uniform 
varieties therefore are the Hevea and 
Manihot. 

The following table gives some idea 
of the relative loss in washing: 

Fine Para (bard or soft)... 12 to 20 percent 

Negrobeads 20 to 40 per cent 

Manitoba 2S to 30 per cent 

Matto Grosso 15 to SO per cent 

Mangabeiro 30 to 35 per cent 

To give some notion as to the 
progress made in the production of 
rubber from South America, the fol- 
lowing facts are interesting: 

In 1825, less than 30 tons of rubber 
were exported ; in 1830 there were 
156 tons; in 1840, 388 tons; in 1850. 
1,467 tons; in 1860, 2,670 tons; and 
in 1897, Brazil alone produced 21,260 
tons. 

From 1909 to 1913, the yearly aver- 
age was between 39,000 "and '40.000 
tons. The May, 1917, issue of the 
" World's Rubber Position " gives 
the following estimate of the world's 
production of rubber in 1916 : 

Plantation 152.650 tons 

Brazilian . 30,500 tons 

Other sources 12.44S tons 

To show the ratio of plantation to 
Brazilian for several years the follow- 
ing data are significant : 

Plantation Wild Rubbers 

Tons Tons 

1010 S.200 40.S0O 

1811 14.410 39,730 

1012 2S.51S 42.410' 

1913 47.618 39.370 

1914 71.380 37.000 

1915 107.S67 37,220 

1916 152.650 36.500 

1917 223.000 52.628 

191S 1S8.000 40.f,L".i 

1919 35S.000 41.635 



CHAPTER III 
African Rubbers, Including Those from Madagascar 



J arieties 

The larger part of the African rub- 
ber trees are of the order Apocyna- 
ceae, of which there are many gen- 
erae but three of these produce the 
majority of the rubber. These are 
Funtumia, Landolphia, and Clitan- 
dra. The rubbers are all more adhe- 
sive but less elastic than Para. 

Of the Funtumia just one species 
is regarded as of commercial value 
and that is the Funtumia elastica. 
The gums from the other species seem 
to be very resinous and the natives 
are thought to use some of these to 
adulterate the better gums. 

The rubber from Funtumia elastia 
when freshly coagulated has a pecu- 
liar sheen to the cut surface and for 
that reason is sometimes called 
" Lagos silk rubber." The main 
varieties of this rubber are what ap- 







*> 



pear in the trade under the names of 
Gold Coast Lump, Ivory Coast Lump, 
Niger Niggers, Benin Lump, and some 
Congo and Cameroon. 

The tree grows best in the province 
of Uganda and the tropical regions 
of Africa. The tree often attains con- 
siderable proportions, in fact trees 
have been found having a circumfer- 
ence of eighty inches and a height of 
one hundred feet, a tree as large as 
the Hevea. 

This rubber is now being obtained 
on the plantation scale by several com- 
panies in Uganda. As a plantation 




Fig. 7 — Tapping Funtumia Ti 



Fig. S 

proposition it has three advantages 
over Hevea. First, it grows more 
rapidly ; second, it yields a larger 
amount of latex for a small number of 
tappings ; third, it is able to withstand 
a comparatively long drought. 

The trees recover rather slowly 
from the wound made by tapping, 
however. Another great objection is 
the fact that the tree has so many 
branches. If planted only a few feet 



11 



RUBBER MANUFACTURE 



apart it will branch down into the 
lower regions of the trunk thus pro- 
ducing a dense bushy mass. A tree 
standing alone branches from the 
ground to the very top. Of course 
these branches interfere with tapping 
and it is found that when they are 
removed by pruning they heal very 
slowly and show bad scars for a long 
time. 

Dr. Christy suggested the planting 
of these trees very closely together 
and then thinning out later. This has 
helped considerably. 

The tapping of the Funtumia is 
done only two or three times a year, 
but it is tapped from the ground up 
to the first branches, generally a dis- 
tance of fifteen to eighteen feet, 

The tapping is of the herring-bone 
type but must be done very carefully 
and must also be very shallow. Dr. 
Christy also suggested that a channel 
be cut in the bark just deep enough 
to carry the latex and that the flow be 
started by means of a pricker. 

This method gives about twice as 
much latex as the Schulz-im-Hofe 
method, which consists of vertical in- 
cisions about four inches apart and 
extending from the ground up to the 
branches. It has also been found that 
if the pricking be done slowly, by 
beginning at the bottom of the chan- 
nel and taking several days to com- 
plete tbe real operation of tapping, 
that a better grade of latex is obtained 
and also a better yield. 

This rubber was first thought to 
be one of the species Kickxia and from 
the Kew Bulletin of 1890 we notice 
the following statement: 

" Tn September, Kew received from 
Captain Denton. C.M.G.. two pieces of 
the frank of ihe I.agos rubber tree, each 
about ten inches to a foot in diameter, 
scarred with tbe marks of tbe rubber 
gatherers. They were sent as tbe 'female' 
rubber tree, a name, we learn, that is 
locally applied to tbe Kickxia africana. 
Bentb. It is thus distinguished from 
JTalarrhena africana. quite a " different 
plant, which is fancifully called the 'male' 
rubber tree. Tbe later is also an Apoc}-- 
naceous plant, but not known to yield any 
rubber. 

•• Should the new rubber Kickxia con- 
tinue of commercial value, there is no 
doubt that it will eventually he possible 
to establish plantations, and thus make 
tbe industry a permanent one. It has 



always been seen that, owing to the climb- 
ing habit of the Landolphia. which hare 
hitherto yielded African rubber, it was 
not practicable to cultivate them in regular 




Fie. 9 — Swahili Climbing Method 

plantations, as they require the support 
of other plants, and when once tapped, 
many years should have to elapse before 
they would be fit to yield another crop. 
With the Eickxia these practical diffi- 
culties disappear. According to Chalot. 
Kickxia africana. has been lately found 
in Gaboon. Specimens have been meas- 
ured which were one meter in circum- 
ference and twelve to fifteen meters high. 
Each tree is estimated to yield annually 
without any injury." 

Wright however, in his Cantor 
Lectures, 1907, points out tbe error 
of the Kew observations, for he says : 

"Funtumia. This genus has lately be- 
come known as a source of rubber in 
Africa. It is still much confused with 
the genus Kickxia, and it is as well 
to again point out that Africa does not 
possess a single species of Kickxia of 
value as a rubber producing plant. Tbe 
four species of Kickxia acknowledged by 
Stapf. are found only in Java. Celebes, 
Philippine Islands, and Borneo. 

"Tbe genus Funtumia is partly African 
nnd is represented by three species. F. 
iastica. Stapf.. F. africana. Stapf.. and 
F. latifolia. Stapf. The species of im- 
portance in Africa is F. clastica, Stapf. 
Its occurrence has been recorded in 
Liberia. Gold Coast. Ashanti. Lower 
Nigeria. Cameroons. Mnndame, French 
Congo. Congo Free States. Uganda. 

" The rubber from this species is very 
valuable, possessing when properly pre- 
pared from eighty to ninety per rent of 



AFRICAN RUBBERS, INCLUDING THOSE FROM MADAGASCAR 



13 




Fin 10 — Tatting a RannTcu Vine 

caoutchouc. Vuntumia ciatstica has been 
described as a tree with a cylindrical 
trunk which attains a height of one hun- 
dred feet ; sometimes the tree occurs more 
abundantly in local areas, and out of an 
area of ahont fifty-four square miles as 
many as one million seven hundred and 
sixty fires have been estimated to oc- 
cur." 

The Manihot Glasiovii lias been in- 
troduced into British Central Africa. 
Tn regard to the advisability of this 
project we find a diversity of opinion, 
some thinking it will prove a fine 
plantation species and others raising 
great objections to it. 

Before taking up the Lahdolphias it 
is necessary to define some of the 
terms which will be used in describ- 
ing these rubbers. 

Ball : The most common form of 
rubber coming from Africa. These 
balls vary in size from an inch or less, 
known as " Small ball," up to four 
inches or more in diameter, and 
known as" Large ball." 

Thimbles: The natives make these 
by cutting the rubber up into small 
cubes, which are sometimes called 
" Nuts," as for example " Ambriz 
nuts." 

Lump: A very common form of 
these rubbers consisting simply of 
large irregular pieces which often be- 
come stuck together in transportation. 



Flake : A form of lump which is 
very soft and is used in frictions. 

Paste: Practically the same as 
flake. 

Strips : Made from lump rubber 
by cutting and pressing before it is 
sold. 

Buttons are made in the same 
manner as strips with the exception 
that they are in small pieces. 

Biscuits and Oysters : The same 
as buttons. 

Niggers and Twist rubbers: A 
form of ball. 

The Landolphias are all creepers or 
vines, yet attain considerable size. 
Often vines are found having a diam- 
ter of six inches. There are several 
species of importance, the Landolphia 
Ownriensis, Landolphia Hendelotii, 
Landolphia 1'hollonii, Landolphia 
Sphaerocarpa, and the Landolphia 
Picrrei. The last two arc found 
largely in Madagascar. 

The rubbers from this species re- 
ferred to in the trade are, Red 
and Black Kassai from the Congo 
region ; Upper Congo balls and Equa- 
teur also from the Congo region ; 
Virgin Sheets and Pinky from Mada- 
gascar ; Sierra Leone Niggers, Twists, 
and Cake all coming from the Sierra 
Leone and southern rivers; Conakry 
Niggers, Soudan Niggers and Twists', 
coming from French West Africa ; the 
Bassam Niggers and Twists likewise 
the Lahou Niggers come from the 
same territory; Liberia Lump, Hard 
Flake and .Soft produced in the 
Sierra Leone district; Accra found 
on the Gold Coast and coming into 
(he market graded as "Prime," 
" Seconds," " Thirds " and lower 
grades of "Flake and Paste"; 
Gaboon, probably the best known 
Flake; Lapori, a Congo rubber and 
represented by Balls, Strips, and 
Cakes, some of the Balls being very 
clean and good. From Angola we ob- 
tain Loanda Thimbles, Niggers, and 
Prima, also Angola Niggers. There 
are several grades coming from the 
port of Mozambique in the form of 
Marbles, Balls, Spindles, and 
Sausage. 

The Clitandra are widely distrib- 
uted throughout Africa. Thpy, too, 



14 



RUBBER MANUFACTURE 



are vines and flourish in great num- 
bers on the Gold Coast and the 
Congo. Their rubber comes into the 
market largely as Lower Congo in the 
form of small cubes. 

In the above we have not mentioned 
all of the varieties of rubber which 
Africa furnishes but we have tried to 
call attention to the representative 
classes of rubber now in use. 

Coagulation 

Concerning the coagulation of these 
African rubbers not a great deal is 
known, in fact we do not know how 
some of them are obtained by the na- 
tives. Therefore we shall describe 
methods in use with the different 
genera rather than with the differeni 
species. 

The latex from the Funtitmia is 
coagulated by boiling and this is the 
method employed by the natives. 
They sometimes use a fusion from the 
leaves of Banhinia reticulate to facili- 
tate the coagulation by heat. This 
rubber when properly prepared is of 
a high grade and possesses great 
strength ; for that reason we have the 
methods used upon the plantations. 
From the Kew Bulletin we get an idea 
of the two most general ways : 

■• There are at present two kinds, 
namely. ' the cold process ' and " the heat 
process." The cold process is chiefly prac- 
tised by the Fanti men introduced from 

the Gold Coast. A cavity is excavated 



in the trunk of a fallen tree so as to 
form a cistern of the capacity necessary 
for holding the milk collected during 
several days. Into this the rubber gath- 
erers pour the milk, after straining it. 
from day to day until it' is quite full. 
It is then covered with palm leaves and 
left for twelve to fourteen days, and 
sometimes much longer, depending on the 
season, until most of the watery portions 
have either evaporated or sunk into the 
wood. 

'"After being kneaded and pressed to- 
gether, the rubber thus obtained has a 
dark brownish color, with the inner por- 
tion-' of a slightly lighter color. Such 
rubber is known locally as 'silk rubber." 

-• The heat process is the one generally 
adopted by the natives of Lagos. This is 
much simpler in working, as it disposes 
of all the milk collected at the close of 
each day. After being strained the milk 
is placed in a vessef and boiled. The 
rubber begins to coagulate almost di- 
rectly the heat is applied and after the 
boiling is over is removed in a somewlial 
sticky condition owing to beiug burnt. 
and of a blackish color. 

" It is pointed out that the heat pro- 
cess, though simpler, impairs the quality 
"f the rubber, and is calculated t" injur. 
The industry. It is probable that if the 
heat process were somewhat modified the 
results would not be so injurious. 

"• An experiment was tried at the Bo- 
tanic station to coagulate the milk by 
heat, but not applied directly to it. The 
result was much more satisfactory. The 
rubier came oft" a milky white color, and 
after being pressed it was clean and firm 
without being sticky. 

"The history of this new rubber in- 
dustry in Lagos is full of interest, and 
illustrates the wonderfully rich resources 
in the vast forests of West Africa. It 




FlG. 11 COACEXATIOX OF I.ATEX AXD PnEPAEIXG SHEETS 



AFRICAN RUBBERS. INCLUDING THOSE FROM MADAGASCAR 



shows also very clearly bow largely these 
resources can be developed by judicious 
and intelligent action 011 tbe part of the 
government." 

Obtaining and Coagulating Latex from J ines 

The methods used by the natives 
for coagulating the latex from vines 
are very diverse. The following 
methods are therefore vised on both 
the Landolphias and the Clitandras: 

It is said that the Red Kassai is 
obtained by smearing the latex over 
the body and the natural heat evapor- 
ating the water the rubber is stripped 
off. The collector after tapping the 
vine collects the latex in his hands 
and smears it over his body, then pro- 
ceeds to his hut where he removes the 
rubber in little bits and makes them 
into Balls. Sometimes after tapping 
the hand is placed against the incision 
and the latex flows down the arm and 
after coagulation this is stripped off 
like a glove. By either one of these 
methods the earthy matter is absent 
but is not absent from the rubbers 
putreseible matter. 

The Black Kassai is obtained by a 
process of boiling and smoking. 

The '" Ball '" rubbers are obtained 
by bruising the vine. In some locali- 
ties as the latex exudes, some salt solu- 



tion is poured over it by means of a 
shell. This coagulates the latex and a 
little lump of rubber is drawn off. 
and by keeping the bruised place 
moistened with the brine the rubber 
is drawn into a thread which is wound 
around and around the original lump 
as a nucleus. 

Very often the natives will start 
five or six such places and then re- 
treat a few steps and wind all of 
these threads into one ball of con- 
venient size to hold in the hands. 
They make large balls of rubber in 
this same manner by taking the ball 
when it has become too large to wind 
in the hands, and lying on their 
backs, supporting it on the stomach 
and continuing to wind it with the 
hands. The salt solution as we 
know is a good antiseptic and there- 
fore this rubber does not as a rule 
develop foul odors, but it does con- 
tain large amounts of occluded water 
and brine which are objectionable. 

Perhaps the most common way of 
obtaining the latex from vines con- 
sists in cutting them down and bleed- 
ing or allowing the vine to dry out 
and then removing the rubber by a 
process of maceration. 

The method mentioned above of 




Fig. 12 — Djsying the Sheets of Rubber 



RUBBER MANUFACTURE 



cutting down the vines and creepers 
which produce rubber and then bleed- 
ing them is very wasteful for a large 
part always remains in the wood. To 
overcome this the Madagascar Rub- 
ber Company, Ltd., has put into op- 
eration the following method: 

They cut down the vines and 
creepers and allow them to dry when 
the rubber which they contain rapidly 
coagulates. The dried material is now 
fed into a machine which grinds it to 
a pulp in the presence of water. 
After leaving this machine it goes 
through several machines called 
" agglomerators " which bring the 
particles of rubber together and at 
the same time wash away the wood 
fibers. This process has effected quite 
a saving in rubber. 

Another method of coagulation by 
natnral heat employed by the natives 
consists in tapping, after cleaning 
away the debris from the ground. 
They then allow the latex to collect in 
the sand which removes part of the 
water by filtration, the remainder 
being evaporated by the heat of the 
sun. The native returns later and 
gathers up the lump of rubber with 
all the foreign matter which adheres 
to it and then delivers it to the buyer. 
This' method is very much preferred 



by the natives for it requires about 
the least amount of labor of any 
method known to them. 

The rubber obtained by this care- 
less method not only contains the for- 
eign matter which it naturally picks 
up and which the native purposely 
adds, but also pockets of occluded 
latex containing nitrogenous matter 
which putrefies and not only injures 
the rubber, but gives it a nauseous 
smell. This method is used largely in 
West Africa and to some extent in the 
Congo and Angola. 

A method also used hi the Congo 
consists in tapping the vine in several 
places, one below the other. At 
the lowest one the native fixes a leaf 
in the form of a trough which will 
conduct the thin stream of latex out 
into a collecting receptacle. The leaf 
is generally made secure either by 
means of clay or partly coagulated 
rubber. The collecting receptacle has 
a hole in the bottom which is care- 
fully corked up. When the latex has 
ceased to flow there is added to it 
four or five times its volume of water 
and it is allowed to stand. The rub- 
ber then comes to the top in the form 
of a semi-solid cream. 

The native then removes the cork 
from the orifice in the bottom of the 




Fig. 13 — Preparing of Ftxtumia Rubber 



AFRICAN RUBBERS. INCLUDING THOSE FROM MADAGASCAR 



17 



container and draws off the lower 
liquid. This contains the majority 

of the putrescible matter. The rub- 
ber is then removed to wooden con- 
tainers where it is exposed to the air 
for some time, depending upon its 
condition. The native judges from its 
appearance when it is ready for 
kneading. If it gets too hard for this 
it is cut up into small parts and is sold 
as ' ' thimbles. ' ' 

This method is open to the same 
criticism as the others ; namely, the 
putrescible matter is enclosed in 
pockets where it decomposes and pro- 
duces a sickening smell. 

The process of using potassium 
alum is in vogue in Africa in just 
about the same manner as in South 
America. 

Citric acid has been used with the 
latex from the Landolphias but it has 
been completely replaced by sulphuric 
acid in Madagascar. Lime juice has 
also been used in a few localities. 
These all have the same objection 
that they coagulate too rapidly and 
thus enclose some of the latex. 

The properties of these African 
rubbers may be summarized as fol- 
lows: Gold Coast Lump, from which 
Strips and Buttons are made, is a 
very good grade of rubber. The, 
Flake, however, is generally wet and 
has a bad odor. Ivory Coast is also 
a good rubber. Niger Niggers at 
first were very poor, suffering a loss 
as high as forty to fifty per cent upon 
washing, but they are coming into bet- 
ter repute at present. 

Benin is generally very dirty and 
has a very bad smell. Congo con- 



tains bark and water, likewise pock- 
eted latex. The Ked Kassai is the 
best rubber from Congo possessing a 
high tensile strength. The black is 
not as good and does not come as 
clean. 

The Sierra Leone comes in several 
grades containing bark and grit but 
low in moisture. Equateur is a much 
esteemed rubber. Bassam Niggers if 
in the form of small balls are good. 
Lahou Niggers are about the same. 
Liberia is wet and a more or less pasty 
rubber. Accra varieties are of a fair 
rank. 

Gaboon is coagulated by an un- 
known process. It is very bulky but 
will take the form of the container 
in which it is shipped. It runs very 
high in moisture. The Lapori is a 
variable rubber as some of it runs in 
good clean condition and some con- 
tains fermented milk. 

The Loanda is gradually disappear- 
ing and its place is taken by Angola 
Niggerheads. The Mozambique rub- 
bers are sold largely in the Liverpool 
market where they are in demand. 
The Pinky from Madagascar is a very 
good rubber, but. due to the reckless 
methods of obtaining it, is liable to 
become extinct. 

From the following table showing 
the loss in washing one may obtain 
an idea of the relative values of these 
African rubbers. 

Red and Black Kassai and Equateur, 6 
to 12 per cent: African Niggers (Sou- 
dan. Conakry. Sierra Leoua, Niger), 15 
to 40 per cent: Madagascar Pinky. IS to 
20 per cent ; Madagascar Niggers. 40 to 
50 per cent. 



CHAPTER IV 



Central American Rubbers 



When we refer to the rubber from 
Central America we generally in- 
clude the territory where we find the 
Castilloas growing. This includes, 
therefore, not only Central Amer- 
ica propei 1 , but also Colombia, Ecua- 
dor and Venezuela, in fact, terri- 
tory north of the Amazon including 
Mexico, yba. a previous chapter we 
mentioned certain rubbers from 
Ecuador and Colombia, but now we 
shall call attention simply to the rub- 
ber obtained from the Castilloas. 

The rubber balls used by the na- 
tives in the game which Columbus and 
the early exploiters found them play- 
ing was of the Castilloa variety. 

Varieties 

• This rubber tree found native in 
Central America and Mexico is called 
Castilloa lactiflua, in honor of Cas- 





FhSSh, 


w*M 


?^|i|iM 


JHra&Bilf 





tillo, a Spanish botanist who died in 
1793 while preparing the flora of 
Mexico. Lactiflua means flowing 
milk, distinguishing it from other 
trees from which the milk exudes but 
does not flow freely. The tree gen- 
erally is called Castilloa elastica. It 
is a significant fact that at one time 
there was more Central American 
rubber used in the United States 
than there was of Para. 1 1 




Fig. 14 — Mexican Rubber Gatherer 



Fig. 15 — Tapping Castilloa 

does not possess the strength, tough- 
ness or elasticity of Para. 
■^ The varieties of rubber from this 
region which are more or less familiar 
to the trade are Guayaquil sheet. 
coming from Ecuador and Colombia ; 



18 



CENTRAL AMERICAN RUBBERS 



there is also some Guayaquil and Car- 
thagena strip, some in the form of 
sausage, and some designated as No. 
1 and No. 2; their production is on 
the decrease at present. 

A grade referred to as Mexico 
comes from Vera Cruz, Tabasco and 
Baraea. Guatemala furnishes a rub- 
ber bearing the same name. These 
rubbers are rather inferior in qual- 
ity. It is thought that they are 
mixed up with cheap molasses, as 
some are very tacky. 

Nicaragua sheets and several grades 
called West Indies, which never fur- 
nish any rubber, along with Nica- 
ragua scrap are familiar rubbers 
from this territory. The Nicaragua 
rcibjjer is generally quite dry but 
rather dirty. The Greytown scrap is 
considered about the best rubber 
from this district. 

In order to encourage the produc- 
tion of rubber the government of 
Nicaragua gives a premium of ten 
cents for every rubber tree planted 
where the number does not go below 
two hundred and fifty planted for 
each person. The trees must be 
planted sixteen feet apart. 

Virgin or Virgen comes in the form 
of strip and sheet and slab. It is 
obtained from a different tree than 
the others mentioned above and is 
used to a great extent in the manu- 
facture of hard rubber. 

Guayule is a rubber from this sec- 
tion unique in its growth and pro- 
duction. 

The above comprise the rubbers 
which we shall consider in this arti- 
cle. The better grades of Centrals 
shrink from 25 to 30 per cent, and 
the remainder from 30 to 40 per cent. 

The method of obtaining the latex 
in use in Central America consists 
in puncturing rather than tapping, 
the tree being punctured higher up 
than is the custom in the case of any 
other species we have considered. 

In order to coagulate the latex the 
native uses some very primitive 
means. For instance, he sometimes 
adds to the latex the juice of the 
" amole " vine. Often this is car- 
ried out in a hole in the ground. 
One pint of amole juice, which is 




Fig. 16 — Coagulating With Vine .Thick 

alkaline in reaction, is added to one 
and a half gallons of latex. In a more 
modern way, after adding the juice 
the whole mass is heated to between 
165 deg. and 175 deg. Falir. By this 
method they are able to obtain sheet. 
The part which dries on the tree 
and is peeled off is called scrap. 

The Coyuntla juice is an astringent 
in nature which will coagulate the 
rubber if the weed which contains 
it is used to whip the latex. 

The natives in some places pour 
the milk from the tree onto mats, 
where it is allowed to dry or evapo- 
rate, then when the rubber is sep- 
arated from the mat a sheet results. 
Several of these sheets are pressed 
together and are then ready for 
market. 

Another method similar to the last 
consists in pouring the latex out onto 
the long, palm-shaped leaves of the 
Oja hlanca which they have dried in 
the sun. 

When the leaves have a coating 
of about a quarter of an inch they 
are piled one above the other and 
pressed to- remove moisture. The 
strips are then separated from the 
leaves, packed into slabs and are 
ready to be transported. 



RUBBER MANUFACTURE 



A very common method of coagula- 
tion in Central America is doubling 
the volume oil the latex with water, 
then allowing it to stand. In a short 
time the rubber comes to the top in 
a creamy consistency. When homo- 
genous enough it is removed, and in 
some localities is placed in the sun to 
dry, while in others it is run through 
between wooden rolls which press out 
the excess water. It is then placed in 
the sun for about fifteen days to dry 
still furl her. This rubber suffers a 
loss of as much as 50 per cent, as it 
contains so much occluded water and 
uncoagulated latex. 

All of these rubbers as prepared 
by the natives arc not of the quality 
which they might be if more care 
was exercised in their production 

Rubber is now being produced from 
the Caslilloa on a plantation scale at 
different places. / To get an idea of 
these plantations, wc shall describe 
the industry as we find it in operation 
by the La Zacnalpa Rubber Planta- 
tion Co. 

The development of the industry 
in Mexico is told in a little book. 



" Rubber, What It Is and How It 
Grows," published by the above 
company. In describing this rubber 
business we shall therefore use ex- 
tracts from this work. 

The lands in Mexico suitable for 
the production of this rubber are lo- 
cated in the states of Vera Cruz, Ta- 
basco, and Chiapas, for the elevation 
above sea level should not exceed 
five hundred feet. The low lands 
along the coast are the best, where 
the soil has a great depth formed by 
the deposits left by the overflowing 
rivers. 

Land for a plantation is generally 
selected which has a. virgin forest 
rather than land which has been un- 
der cultivation. It must be capable 
of perfect drainage and yet pro- 
tected from overflowing rivers. In 
the above mentioned plantation 
there are over ten thousand acres of 
trees, averaging about four hundred 
trees to the acre. These trees attain 
a height of from fort}' to fifty feet 
and a diameter of about twenty 
inches. 

The Castilloa begins to blossom 




Pig. 17 — Preparing Rubber on Oja Blanca Leaves 
Spreading Latex on Leaf Pressing Out Moisture 



CENTRAL AMERICAN RUBBERS 




Fig. 19 — Prepaking Rubi 
Removing Rubber Sheet 

when it is between five and six years 
old. Before blooming it sheds all of 
its leaves, this taking place between 
January and April. When the seed 
is ripened the tree puts forth new 
leaves. 

The planting of these trees is very 
interesting. The land is first sur- 
veyed into tracts of thirty-three 
acres, including avenues and streets ; 
the roads running north and south 
are called avenues and are named, 
while the ones running east and west 
are called streets and are numbered. 

The land is cleared by cutting 
down the forest, and is then burnt 
over. It is then staked out to allow 
four hundred trees to the acre, and 
at each stake a mound of earth is 
made and the rubber seed planted, 
which germinates in from eight to fif- 
teen days and grows quite rapidly. 

After planting, a great amount of 
work is required to keep the natural ' 
vegetation from choking out these 
tender trees. After about two years 
the tree requires very little atten- 
tion. The tapping begins when the 



Blanc a Leaves 

The Finished Sheet . 

tree is between five and six years old. 

The old method consisted in mak- 
ing a V-shaped incision in the tree 
and placing a leaf under this to 
serve as a funnel and conduct the 
milk into a hole in the ground made 
at the foot of the tree. This hole 
was lined with green leaves. In a 
short time the latex coagulates on 
the edges of the incision and stops 
the flow. This is removed as often 
as necessary until the milk ceases to 
run. 

To tap twelve trees and obtain 
their full quota of latex is regarded 
as a day's work for one laborer. 
When the flow has stopped the tap- 
per carefully removes the leaves con- 
taining the latex from the hole and 
pours it into his gathering recepta- 
cle. It is a very wasteful method at 
best. When some of these trees are 
first tupped the milk will spurt out 
some distance, just as though it were 
under pressure in the tree. J 

The new method of tapping we 
shall take from the book referred to 
above. 



22 



RUBBER MANUFACTURE 



" The hulero, or rubber gatherer, is sup- 
plied with a tool invente'd and perfected 
on La Zacualpa Plantation, consisting of 
a stout handle, twelve inches long, at one 
end of which a U-shaped sheet of steel is 
fastened ; just forward of this U, the 
curved portion of which is sharpened to a 
keen edge, a metal finger is depressed 
more or less as desired by an adjustable 
screw which runs through the handle : 
and the ' set ' or ' adjustment ' of this fin- 
ger, which slides over the surface of the 
bark as the tool is drawn across the tree, 
determines the depth of the cut made by 
the U-shaped knife which follows imme- 
diately behind the metal finger. 

" A deeper or shallower- cut may be 
made according to the size of the tree 
which we are tapping and the thickness 
of the bark; and we can effectually 
guard against cutting through the bark 
and into the wood of the tree. The latex, 
or rubber-producing milk, flows in veins 
in the bark only, and is entirely distinct 
from the life sap of the tree which flows 
between the bark and the wood. It is im- 
possible to avoid cutting into the wood 
when the machete is used, and it is from 
the machete's too deep cutting that injury 
to the tree results. 

" With our perfected tapping tool a 
smooth continuous channel is cut across 
the tree's trunk and a canal is made which 
cannot fail to conduct the latex to a re- 
ceptacle placed to receive it ; while the 
succession of hackings made by the ma- 
chete are often out of line and much of 
the latex flowing along the cuts leaves the 
line of travel and is lost." 

The method of treating the latex 



on the plantation is quite different 
from the wasteful and dirty ways of 
the natives. The exact process of co- 
agulation is kept secret, but after it is 
coagulated the rubber is washed 
through a modern washer, sheeted 
and hung up to dry, then by means 
of a hydraulic press these sheets are 
made into solid blocks of about twen- 
ty-live pounds each, when the process 
is complete. 

In Jlexieo a shrub is found which 
produces rubber and is not known to 
grow in any other locality. A care- 
ful study of this plant has been made 
by Francis Ernest Lloyd, Professor 
of Plant Physiology, Alabama Poly- 
technic Institute, and from his ac- 
count we get a good idea of this par- 
ticular rubber plant. It bears the 
name Guayule (Parthenium argenia- 
tum) and flourishes on the Chib.ua- 
huan Desei't. 

It was discovered .by J. M. Bige- 
low in 1852, while attached to the 
Mexican Boundary Survey, and 
was first described by Prof. Asa 
rubber was first obtained from it by 
the natives by chewing the bark and 
then collecting the rubber together in 
a ball. 

This method of getting the rubber 







Fig. 20 — Dexse Growth of Guayct.e 



CENTRAL AMERICAN RUBBERS 




Fig. 20 — A Guayule Extracting Factorv 



dates back a great many years. To 
substantiate this belief Professor R. 
H. Forbes furnished the following 
information : 

" The lump of rubber, a portion of which 
I recently handed you, was found in De- 
cember (or thereabouts), 1909, at the 
west end of the Santa Cruz Reservoir and 
Land Company's dam, 14 miles west of 
Sasco, Ariz. C. O. Austin, who was pres- 
ent, states that this ball of rubber was 
contained in a small olla with articles of 
stone belonging to the older prehistoric 
rains of the country. 

" The find was made at about three feet 
below the general surface which was 
formed by the off-wash of an adjacent low 
mountain. No traces of houses on the 
present level of the land, according to Mr. 
Austin, were visible. One other ball of 
rubber was found here, and is now in 
Col. W. C. Greene's collection at Cananea. 
I regard this find as genuine, as Mr. Aus- 
tin is familiar with Salt River Valley 
ruins and his statements are confirmed 
by others." 

Because of the resinous content of 
this plant it burns rapidly, and large 
quantities of it have been used in 
Mexico as fuel in smelting. 

About the first move to utilize this 
rubber was in 1888, when a company 
sent an agent into Mexico with in- 
structions to obtain some of this 
" rubber bark." He carried out his 
orders carefully and had shipped to 
New York 100,000 lb. of the entire 
shrub. The freight on this large 
amount of wood so discouraged this 
company that further efforts to obtain 



this rubber were not undertaken im- 
mediately. 

In 1902 a factory was built at Ji- 
mulco for the extraction of this rub- 
ber. A little later a large factory 
was built at Torreon bj' the Conti- 
nental-Mexican Rubber Co. Since 
this several large factories have been 
built for extracting the rubber out of 
the shrub. 

The methods used for extraction of 
this rubber are interesting, for they 
are different from any mentioned 
thus far; something like it was out- 
lined in connection with the Lan- 
dolphias, however. 

The methods differ because the 
rubber which the plant contains can- 
not be removed by bleeding, for it 
exists as rubber in the cells of the 
plant itself. There are two gen- 
eral methods which have been and 
are being used. The first consists 
in dissolving the rubber by means of 
chemicals after the shrub has been 
subjected to preliminary grinding. 

The other method consists in ag- 
glomerating the rubber mechanically 
after it has gone through the prelim- 
inary grinding. This method has just 
about been abandoned, as it is impos- 
sible for it to compete with the 
mechanical method. The first process 
consists in extracting the rubber from 
the ground shrub by means of naph- 
tha. The resulting solution is then 



RUBBER MANUFACTURE 







9". jK^^H* TVj 




% 




Jqlaftlt)\ i ^^■■nnMBk.'VH 















Fig. 21 — Upfer Floor in Guaylle Factory 



partly distilled, after which alkali is 
added. This holds the resins in solu- 
tion and the rubber separates out. 

In the other method the shrub is 
pulled up root and all and brought 
to the store houses for a short period 
of seasoning, as it seems to work 
better after such treatment. In the 
more improved process instead of pull- 
ing up the shrub it is cut off at the 
ground, and this allows it to send up 
sprouts, which in time will produce 
rubber. 

From the store houses it is taken 
and washed to remove dust and sand 
which would adhere to the rubber 



and increase its specific gravity. It 
is then passed between corrugated 
rolls, running differentially, which 
cut the shrub and grind it at the same 
time. 

The mass is then passed into a peb- 
ble mill, the charge generally con- 
sisting of one-third its volume of 
pebbles, one-half of water, and from 
six to eight bushels of shrub. The 
mill rotates at the rate of thirty 
revolutions to the minute for from 
ninety minutes to two hours, when 
there results a fine pulp mixed with 
little particles of rubber. 

This is separated as well as possi- 




Fig. 22 — Troughs to Coliect Extract From Plants 



CENTRAL AMERICAN RUBBERS 



25 



ble from the dirty water which it con- 
tains and then transferred to settling 
tanks. The rubber then comes to the 
top and is removed by skimming, 
thus separating it from most of the 
fiber, which water-logs and sinks. 
To clean the rubber still further it is 
often put through a beater-washer 
and scrubbed for some time, when it 
goes between corrugated rolls again 
and scrubbed for some time, when it 
sheet it and make it ready for the 
market. This rubber contains about 
'25 per cent of moisture. 

In some places they take this rub- 
ber just as it comes from the set- 
tling tanks and boil it with a 1 or 
2 per cent, solution of caustic soda, 



which will separate the rubber more 
completely from the fiber, and will 
also reduce the per cent, of resin 
which normaUy runs about 25 per 
cent. The resin has also been re- 
moved by extracting the Guayule 
with hot acetone. 

According to Weber, the Centrals 
suffer the following commercial 
losses : 

Per cent. 

Guayaquil (sheet I 20 to 30 

Guayaquil, Carthageua (strip) .. .20 to 30 

Mexico 12 to 15 

Guatemala 25 to 35 

Nicaragua (sheet I 10 to 15 

Nicaragua (scrap) 10 to 15 

Virgin sheets 12 to 15 

Guayule 30 



CHAPTER V 



Rubber Plantations and Their Development 



When we consider plantation rub- 
ber our attention and thought are 
directed to that produced in Ceylon, 
the Federated Malay States. Dutch 
East Indies. Borneo, and the Pacific 
Islands. In this chapter we shall con- 
sider the establishment and mainte- 
nance of the rubber business in these 
areas. 

The tree which is now almost exclu- 
sively planted upon these plantations, 
and thus furnishes the rubber, is the 
Hevea, the descendant of the tree 
which was first found in South Amer- 
ica. 

It was Herbert Wright who in 1834 
suggested that it would be profitable 
to plant some of the best species of 
rubber producing trees in the East 
and West Indies, for even at this time 
Hancock, who was experimenting with 
rubber, was having difficulty in ob- 
taining the crude rubber. 

The real plantation industry as we 
know it. however, dates from the 
work of Sir Joseph Hooker, director 
of the Royal Gardens at Kew. Sir 
Clements Maxkham, connected with 
the India Office, and Collins. Cross 
and Wieknian. who made excursions 
collecting material. 

In 1S73 Collins obtained some seeds 
of the Hevea from the Amazon region 
and took them to Kew. In 1S75 he 
collected some from the Castilloa and 
after many trials and hardships suc- 
ceeded in landing these at Kew. In 
1S77 he obtained more seeds from the 
Hevea and no doubt some of the trees 
in the East to-day are direct descend- 
ants from these seeds. 

In 1S76 H. A. ^Viekman. who was 
living in the rubber region of the 
Amazon, was commissioned by the 
Indian Government to obtain a sup- 
ply of Hevea seeds. The Govern- 



ment of Brazil was opposed to the 
shipping of these out of the country. 

Wickman fortunately had the op- 
portunity to charter a large steamer 
which had given up her cargo and 
was about to return empty. This he 
did and with the aid of all the laborers 
he was able to get he started out to 
collect the seeds. They succeeded in 
obtaining the supply and the cargo 
was passed as one of " botanical 
specimens. ! ' It contained many thou- 
sand seeds. These were also taken 
to Kew. and when planted only about 
four per cent germinated. 

Although the Indian Govern- 
ment financed the undertaking they 
selected Ceylon as the proper plaee 
to carry out the experiment. The 
principal nursery for trees ill Ceylon 
was located at Henaratgoda. Dr. 
Trimen was in charge of the gardens 
and in 1SS1 the first flowers were seen 
upon these trees. 

In 1884 there were over one thou- 
sand trees there but in 1SS5 the num- 
ber was considerably reduced owing 
to the necessity of thinning out. 

In 1S93 over ninety thousand seeds 
were distributed to planters in Cey- 
lon. Malaya and elsewhere. 

Trimen made the first experiments 
on tapping planted rubber trees in 
1SSS and came to the conclusion that 
a big profit could be realized. 

To show how the industry has 
grown the following figures might be 
interesting : 

Ceylon 

In 1890 about 300 acres had been 
planted : in 1900 about 1.750 acres : in 
1904 about 11.000 acres : in 1906 about 

100.000 acres, which in 1912 was in- 
creased to 230.000 acres and in 1913 
showed an acreage of 235.000 : at pres- 
ent 250.000 acres have been planted. 



RUBBER PLANTATIONS AND THEIR DEVELOPMENT 




Fig. 23 — Hevea Seedlings Ready for Planting 



Malaya 

In 1897 about 350 acres had been 
planted; in 1906 about 100.000 acres 
were under cultivation : in 1912 about 
620,000 acres had been planted. This 
showed a further increase in 1913 to 
667.000, and is still growing. 

Notice how rapidly the industry de- 
veloped in Malaya. 

In Java there are probably about 
150,000 acres planted, and in Sumatra 
about 70.000 acres. 

A table showing the production of 
rubber from Ceylon and Malaya is 
interesting : 

Ceylon Malaya 

1'eak. Exports. Exports. 

Tons. Tons. 

1906 147 425 

1907 248 1.036 

190S 407 1.6G5 

1909 666 3,340 

1910 1,472 6,500 

1911 2.90O 11.000 

1912 6.697 1S.956 

1914 15,335 50,404 

1915 21.785 79.415 

1916 24.334 111,394 

1917 32.289 153,024 

191.8 21,080 140,659 

1919 37.351 240,109 

This gives some idea of the great 
business which has grown up so 
quickly. 

Now we will trace more in detail 
how these large plantations have been 
established. 



The Hevea was found to grow in a 
belt which is included within ten 
degrees of the Equator, provided 
there was plenty of moisture. Al- 
though it flourishes best on the low- 
lands, it is found giving good returns 
at an elevation of twenty-five hundred 
feet. It will grow in comparatively 
dry districts if it is protected from 
the wind, but of course the growth is 
slower and a longer period of time 
is taken before it is ready to produce 
any rubber. 

As a general rule, we» might say 
that rubber could be produced on 
almost any soil in the latitude of 
Ceylon up to an elevation of two thou- 
sand feet, provided the soil receives 
at least seventy-five inches of rain- 
fall a year. It is found that Hevea 
does best upon soil where virgin for 
ests have been removed. 

Planting Rubber Trees 

Before planting, therefore, a great 
amount of work must be done to clear 
the land. This is done by cutting 
down the trees and underbrush and 
then burning it over when it is dry. 
In some localities, the stumps are re- 
moved by means of dynamite. It is 
found best to remove all dead wood 




C: 



RUBBER MANUFACTURE 



and not allow it to rot upon the 
ground, for that removes the in- 
- - danger of the young :: s be- 
ing attacked by white ants and root 

seases. After this land is cleared, 
it requires a vast amount of labor to 
keep down the weeds which imme- 
diately spring up. 

_ nurseries must be established 
to supply the plantations with plants 
which must be at least a year old 
when set out. The selection of the 
site for the nursery is an important 
It must be close to the fields 
where the plants will be used and it 
must be in rich soil with plenty of 
moisture and protected from the 
winds. It is not always an easy mat- 
ter to find such a sit 

When planting the seeds, plenty of 
room must be allowed for the plant 
to grow. Generally seeds are placed 
at a distance of no less than six by six 
al times the actual num- 
ber of plants needed should be raised 
so that only the best may be used. 
3 the great disadvantage in the 
method of planting - s at stake 
where the plant remains whether good 
or bad. 

In the Malay States they often 
plant the seeds in individual baskets 
which are later taken to the planta- 
tion with the seedlings and planted 
without disturbing the plant in the 



least. This has the same objection 
as the method of planting at the stake. 

The same area should never be used 
over as a nursery unless it has been 
thoroughly dug up. limed and then 
allowed to remain fallow for some 
time. This is done to destroy all the 
insect • ests 

Planters have learned to realize 
that great care should be exercised in 
selecting the seed. "When a breeder of 
cattle is desirous of producing beef 
cattle he selects the largest of his cat- 
tle to produce this strain, and. by con- 
tinued selection, he arrives at the de- 
sired result. If. on the other hand, he 
wishes to build up a fine dairy he se- 
lects the ones from which he gets the 
:ailk. and. by con- 
tinued selection of this sort, arrives at 
a different result. So it should be in 
the selection of seed to produce the 
rubber plantation. 

In the past the planters have 
striven to obtain their seeds from the* 
oldest trees regardless of whether 
they produced much latex or not, and 
it has been found that trees will vary 
as much in their yield of latex as cows 
will in their production of milk. It 
is, therefore, best to collect the seed 
from the trees which produce the most 
latex, r^eryrhing else being equal. 

It is not an easy task on a large 
plantation to pick out a tree here and 




M — ttszhdcg Yorx6 Rttbbee 



KIBBFR PLANTATIONS AND THEIR DEVELOPMENT 



there aud then collect seed from these 
trees only. So it has been recom- 
mended that certain areas of a planta- 
tion be set aside for producing the 
seed for future plantations; that 
these trees all be tapped in the same 
manner and at the same time ami the 
yield of each tree carefully kept. 

After ascertaining which are the 
I 'est trees the others are cut down 
and their stumps are drawn out. 
When the time for producing seed 
arrives the tapping' is stopped and 
the seed allowed to develop and is 
then collected. In this way only seed 
from the best yielding tree will be 
used and thus future plantations 
should produce more rubber than the 
present ones, which have been propa : 
gated from seeds taken from the oldest 
trees regardless of yield. 

As to drainage there are two dis- 
tinct kinds. In the Malay States the 
rubber is planted on the low alluvial 
deposits where the water level is only 
a foot or two below the surfaee of the 
soil : while in parts of Ceylon and 
other territories the trees are planted 
upon steep hillsides. 

In the first case the water must be 
removed to a river or the sea, and this 
is effected by a system of canals cut 
through the plantations. This work 
sometimes is done by the govern- 
ment before the land is leased or sold 
for plantation purposes, but generally 
it must be done by the promoters 
themselves. In some localities the 
canals must be very frequent, in fact 
between the rows of trees, and the 
trees are really planted 'upon the 
earth throw), out in the digging of the 
canals. 

In the second system drains are not 
cut so that the water will be removed, 
for the natural slope will take care 
of that, but in such a way that the 
water will be removed so as not to 
wash away the soil so rapidly. To do 
this small ditches are cut across the 
slopes with a gentle fall and are car- 
ried along until they enter a natural 
ravine. The number of such drains is 
dependent upon the slope of the land ; 
of course the steeper the slope the 
shorter the distance between them. 

Irrigation has been little practiced 



as the few attempts thus far made 
have been failures. 

The number of trees to the acre has 
been a much debated question, some 
contending that best returns are ob- 
tained from three hundred trees to 
the acre and others claiming as low 
as fifty, and between these limits we 
find every conceivable number recom- 
mended. 

If the trees are planted 12 by 12 
feet apart we find three hundred to 
the acre: if 30 by 30 feet apart then 
fifty to the acre. If the trees are 
planted close together, during their 
early years of tapping they are not 
crowded and of course more trees are 
producing, but as they get older and 
do become crowded, then their yield 
when it should have increased will bo 
found to decrease and the advantage 
is in favor of the trees farther apart." 
It is generally thought at this time 
that 150 trees to the acre give the 
best results, though we have not had 
enough experimental data along this 
line as yet. 

The planting is done in holes about 
a foot and a half deep at least, the 
larger the hole the better. In some 
places the holes are made and the 
ground loosened by the use of 
dynamite. 

When planting, the ground is 
tamped in tightly around the seedling 
and in some places they are stumped, 
that is the whole top is cut away leav- 
ing just a stump. The roots are also 
cut off short and the tap root is 
severed. This planting is done dur- 
ing the rainy season, and even then 
the young trees are middled to pro- 
tect them in case of drought. 

The trees grow very rapidly. In 
Ceylon a licvea will grow from six 
to nine feet a year during the first few 
years and its girth will increase at 
the rate of three or four inches a 
year. The greatest growth takes place 
after the third year until the branches 
become very thick: then it grows 
more slowly. 

In the Malay States the growth 
is more rapid and a four years' 
growth there is equivalent to a five 
years' growth in Ceylon. Some trees 
in Cevlon that are about fhirtv-six 



RUBBER MANUFACTURE 




RUBBER PLANTATIONS AND THEIR DEVELOPMENT 



years old have attained a height of 
eighty-live feet. 

Cultivating the Land 

The weeding which follows the 
planting is a vexing problem to 
the planter. A great deal of it of 
necessity must be done by hand. 
Some harrows drawn by oxen are 
used but the systems of drainage and 
unevenness of the ground makes it 
almost impossible to use any of the 
modern machines which recommend 
themselves for such work. There- 
fore large numbers of coolies are em- 
ployed to remove the weeds. 

As soon as the job is completed 
once they must turn right around and 
go over it again, for it becomes a 
very expensive operation if the weeds 
once get the start of the weeders. It 
is necessary to remove the weeds not' 
only because they choke the young 
seedlings but in case of a drought 
they rob the trees of the moisture 
which is imperative for their growth. 

While the trees are young and of 
course non-productive it has been 
suggested that some other smaller 
crop be grown between the trees. 
This practice is called " intercrop- 
ping." Tea has been raised and also 
coffee. Indigo has been recommended 
and at first thought seems reasonable 
as it is a leguminous plant and thus 
collects nitrogen from the air. But 
the synthetic indigo has driven the- 
natural product out of the market. 

Many are of the opinion, however, 
that intercropping is a bad practice, 
as it checks the growth of the trees 
and what is gained from the inter- 
crop is lost when it comes to the main 
industry, the production of rubber. 
When an intercrop is cultivated and 
then dies as a result of the trees' 
shade it must all be cleared away so 
that it does not furnish a center for 
the development of fungus diseases. 

The use of artificial fertilizers is 
believed to be advantageous. Potash 
has been found to produce a better 
growth in the tree and also seems to 
help the renewal of bark where it has 
been removed in tapping. 

Too much nitrogen is a bad thing 
as it tends to make the trees brittle 
and also top-heavy. Nitrogen is 



necessary for plant growth and is the 
most expensive to supply to the soil 
in commercial fertilizers. To obtain 
nitrogen in soils which have become 
depleted, therefore, they resort to 
what is known as ' ' green manuring. ' ' 
Leguminous plants are sowed broad- 
cast over the freshly cultivated 
ground. These plants as they grow 
take up nitrogen from the air and 
make it available for plant use. These 
plants must be cut at the proper 
stage, however, generally at intervals 
of from four to five months. 

As the trees grow larger there 
comes the question of pruning and 
thinning. Very little pruning is done 
other than to remove the dead 
branches or ones that are found low 
down on the trunks of the trees which 
have been planted far apart. 

Thinning presents a serious prob- 
lem. Just what trees shall be re- 
moved? Of course, the weakest ones 
or those diseased should be cut down, 
but this often breaks up the regularity 
in the spacing of the trees. A careful 
record of each tree should be kept and 
those yielding the largest amount of 
latex should always be kept, regard- 
less of position in the plantation. Here 
again all signs of the removed trees 
must be destroyed. 

Tapping the Trees 

At the age of from four to six years 
the trees have become large enough to 
be tapped and begin to yield a small 
return. At this age the workers go 
through the plantation and measure 
the trees to ascertain what ones are 
suitable for tapping. Any tree which 
has a girth of eighteen inches three 
feet above the ground is marked for 
tapping. Trees of this size have bark 
thick enough so that it will renew and 
the tapping will not permanently in- 
jure the tree. 

After the trees are selected for 
tapping the operation becomes purely 
a routine one. The laborer starts out 
early in the morning and taps the 
trees allotted to him, at this time plac- 
ing the little cups in position to col- 
lect the latex. 

When the trees are through run- 
ning, which is determined by sending 
out inspectors, the tapper then re- 



RUBBER MANUFACTURE 



visits the trees which he tapped, tak- 
ing with him two large enameled 
buckets. Into the one he pours the 
latex from the cups; in the other 
bucket he has a small amount of 
water in which he washes the cup and 
inverts it beside the tree so that it 
will be clean and ready for the nest 
day's use. 

When this is clone he takes his latex 
to the central collecting station or in 
some cases directly to the coagulating 
house. This in brief constitutes the 
routine life of a rubber gatherer. 

The different methods of tapping 
on the plantation have been studied to 
some extent. There are two general 
terms in use for this. " Incision " is 
done by puncturing the bark, while 
" excision " means the removing of 
some of the bark. 

Several " incision " methods have 
been used and are still in use. There 
was at first a practice copied after 
the natives' method, of making a 
large gash in the tree. Later two 
gashes were joined together in the 
shape of a V. 

Then the practice of pricking the 
bark was tried. A good flow of 




Fig. 26 — Marking Trees for Tapping 



latex was secured and the recovery 
was rapid, but it took too much time 
to perform the tapping and the latex 
was difficult to collect. The former 
difficult}- was removed when Bowman 
recommended his rotating spur- 
shaped pricker. A single stroke with 
one of these tools would make a row 
of incisions running across the bark 
of the tree. The latex was hard to 
collect so they combined this method 
with the one of making a shallow 
channel in the bark to carry the latex. 
This however seems to injure the 
trees. 

In Ceylon they tried tapping by 
use of the herring-bone system where 
each rib was not a channel but four 
ribs made by a pricker. With the aid 
of a tapper, the latex can be made 
first to follow 7 into the central channel 
and thus be collected. 

Bamber suggested a method of inci- 
sion which produces large quantities 
of latex. Pie made two vertical chan- 
nels on opposite sides of the tree: 
then, beginning at the top, lie made 
transverse cuts from one to the other 
extending to the bottom. He would 
skip a day then make his vertical 
sections an inch to the right of the 
original ones and tap the tree in tin- 
same manner. This was repeated 
until the whole circumference of the 
tree had been tapped. This method 
lias the objection first of consuming 
a large amount of time ; second, that 
the trees when fully tapped must be 
allowed a rest period ; and third, that 
a large amount of rubber coagulates 
on the tree and must be collected as 
scrap. 

At present nearly all the tapping 
is done by " : excision " methods, or 
the removing of the bark. 

The exact time depends somewhat 
upon the length of time given for the 
removal of the bark. Four years 
seems to be the average time allowed 
for this, although there is a common 
belief that a longer time should be 
allowed. But when four years is de- 
cided upon, the circumference of the 
tree is divided into four equal parts, 
and each quarter tapped by the half- 
herring-bone method. Each quarter 
then represents a year's tapping. To 
preserve the symmetry of the tree the 



RUBBER PLANTATIONS AND THEIR DEVELOPMENT 



33 



quarter opposite the one first tapped 
is tapped the second year and the 
other two sections in successive years. 
To mark the tree for tapping, a 
horizontal line is marked around the 
tree about four feet from the ground. 
From this line just five inches apart, 
if the tree has a girth of twenty 
inches at this point, two vertical lines 
are marked down the tree. Then five 
inches down on one line, a point is 
marked and, when a line is drawn 
from this point to the intersection 
of the other vertical line with the 



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V mm 




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JafifiE £> 


mP^'SB! 


V it 


WM 


ft 1 


BiilWKr 1 JBMBkBJ 


IK /^fl 




m m 




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Fig. 27 — Half-Herringbone Tapping 

horizontal one, it makes an angle of 
45 deg. with the vertical ones. This 
establishes the angle for cutting and 
removing the bark. 

The one vertical line is now made a 
broad deep channel for conducting 
the latex, and the other is made deep 
enough to preserve the limits of the 
year's tapping. Along the oblique 
line, a groove is cut deep enough to 
allow the latex to flow and not to in- 
jure the cambium. 



That operation constitutes the first 
tapping. On alternate days gen- 
erally another thin slice of bark is 
removed from the lower edge and thus 
the process goes on until the season 
of tapping is over and by that time 
the bark has been removed from this 
quarter of the tree. Great skill is 
acquired by some of the workers in 
this form of tapping. From the fol- 
lowing table some idea of the amount 
of rubber produced per acre can be 
gained : 

Age , CEYLON. N ^-MALAYAN.—, 

of trees. Per acre. Per tree. Per acre. Per tree. 

Years. Lbs. Lbs. Lbs. Lbs. 

4-5 50 .4 100 .8 

5-6 100 .G 150 1.0 

6-7 150 .8 200 1.3 

7-8 200 1.2 250 1.6 

S-9 250 1.5 350 2.2 

9-10 300 1.9 400 2.5 

(This table is taken from tlie report of R. II. 
Lock.) 

Coagulating the Latex 

We shall next discuss the handling 
of the latex which generally contains 
about thirty-five per cent caoutchouc. 
This latex is brought into the place of 
coagulation either in large enameled 
buckets on the heads of the gatherers 
or it may be brought by them simply 
to a collecting station in this manner 
and from there sent by a railroad sys- 
tem to the factory for treatment. 

The first process is that of coagula- 
tion. 

The substance used to the greatest 
extent for this purpose is acetic acid. 
It is said that 99^4 per cent of the 
plantation rubber is coagulated by 
this reagent. The amount to be used 
varies considerably but fortunately it 
may be used through quite a range 
and not impair the rubber. 

Some one has suggested that an 
indicator like litmus be added to the 
latex, which is alkaline, then add the 
acid until it shows an acid reaction. 
This has not been found to work 
satisfactorily in the hands of inex- 
perienced labor. Then too the latex 
varies and in some instances that 
amount of acid is not sufficient to 
cause coagulation as rapidly as 
desirous. 

The safest rule is to make pre- 
liminary tests on each batch of latex 
and thus ascertain just how much 
acid is required to produce the best 
results. No rule of thumb is found 



RUBBER MANUFACTURE 



to work in all eases. Perkin recom- 
mended the use of one part of acetic 
acid to eleven hundred parts of latex. 

The acid is first measured out and 
then diluted with water when it is 
added to the strained latex and 
thoroughly stirred, then allowed to 
stand for a length of time depending 
upon what form the finished rubber is 
to be in. 

If crepe is being made the spongy 
rubber is removed after it has stood 
about half an hour and is transferred 
to a washing machine. 

If sheet is to be made it is coagu- 
lated in shallow pans. These are 
allowed to stand until the rubber is 
firm and can be removed in one sheet. 
This generally takes several hours. 
These sheets are then passed between 
smooth rolls running at the same rate 
with a stream of Avater playing over 
them. This is to remove the traces of 
acid which remain after the coagu- 
lation. 

When preparing crepe the washing 
is done upon a machine which has 
corrugated rolls and these run at dif- 
ferent speeds. The rubber comes out 
in a long lace-like strip which will 
dry quickly and is then ready for 
packing. 

The drying is done by one of two 
methods. The rubber may be hung in 
an airy room, from which the light 
must be excluded, and alloAved to re- 
main there until it is dry. "In moist 
climates this takes a long period of 
time. To shorten the time hot air has 
been blown into these rooms, and thus 
the drying hastened. Prolonged ex- 
posure of the rubber, however, to a 
high temperature often renders it 
tacky. 

As a still quicker method vacuum 
driers have been used. Some manu- 
facturers contend that the life or 
nerve of the rubber is killed by dry- 
ing in a, vacuum. This, however, is a 
debatable question. 

The crepe after being vacuum dried 
is then run through a machine which 
you might say recrepes it, for the 
vacuum drier tends to make it fluffy. 
In some places in connection with the 
slow drying' process they have imi- 
tated the smoked rubber from South 



America by blowing the smoke from 
burning green wood or cocoanut husks 
into the drying rooms where either 
the crepe or sheets may be hanging. 
Rubber treated in this manner is 
known as smoked crepe or sheet and 
has been at a premium in the market. 

Machines and methods for smoking 
the latex directly have been patented 
from time to time but as yet none of 
these are used to any extent. 

Block rubber is made by pressing 
together either smoked or unsmoked 
sheet or crepe. In this form it is 
handled conveniently but when it 
comes to the factory for use it must 
be cut up, which takes labor, and then 
too it may contain objectionable sub- 
stances in its interior. 

The highest grade of rubber is pre- 
pared from strained latex and is 
known as first latex rubber. 

On the large plantations the scrap, 
that which is coagulated upon the 
trees and collecting receptacles, is 
worked up first on maseerating ma- 
chines, then washed and comes out in 
a form of crepe which is graded ac- 
cording to its color. 

Tree Diseases and Other Pests 

It is well perhaps that we should 
call attention to some of the pests 
with which the rubber planter must 
contend. 

The one that causes most trouble is 
one over which man has not much 
control, namely the wind. Hevea 
trees cannot be grown in wind-swept 
districts unless the planter is able to 
establish a barrier or wind break. 

The animals which are a great 
nuisance are elephants, deer, cattle, 
pigs, monkeys, and porcupines. If 
you will observe this list carefully 
you will undoubtedly come to the con- 
clusion that it would be a difficult 
task to fence against such a menagerie 
as this. 

Not much damage is done to the 
Hevea by boring insects as the pres- 
ence of the latex protects the trees 
from their attack. If a fungus 
growth should kill the bark in cer- 
tain areas then some stinging insects 
will attack the tree at these places. 

A species of white ants, however. 



RUBBER PLANTATIONS AND THEIR DEVELOPMENT 



ii l\ h 

1 •- i: 


•■^^^^^^^ i -2« 








fflsMlnnn 


■ mm { l 

111 


Eq 

■i 




\ t -■ 


? f « 111 

1^" 




m 1 Sg 




' ft 

■ . . 

j 


i 



Fig. 2S — Factory on Rubber Plantation 



must be carefully watched for. They 
attack the roots of the tree and then 
•eat out the interior. Their presence 
remains very often unsuspected until 
the leaves of an apparently health}' 
tree all at once wither. They can be 
discovered by digging a small trench 
around the tree and noticing whether 
there are any passage ways leading 
out- to their nest which is always lo- 
cated a little distance from their food 
supply. The fumes of sulphur and 
white arsenic will kill them. 

There is a slug which seems to 
flourish upon the latex of these trees 
and often does considerable damage. 
Painting a band of tar about the tree 
is sufficient to guard against this pest. 

The greatest pests to the planter 
are those of a fungus growth. Some 
attack the roots, some the stem and 
branches and even the fruit. 

The fungi which attack the roots 
are the hardest to deal with. Gen- 
erally their presence is not discovered 
until a few trees are blown down due 
to the killing of the roots. All af- 
fected trees must be destroyed and 
lime forked into the soil. This treat- 
ment will kill the pest. 

The diseases of the stem are called 
canker. They are fungi which de- 
velop under the bark and tend to 
destroy it in such a way that it softens 
and rots. As soon as it is discovered 



it should all be cut away and then 
the tree if allowed to rest will heal 
over the infected area. This same 
fungus will spread over the tree and 
attack the seed pods causing them to 
rot also. 

" Pink disease " and " die-black " 
are terms familiar on the plantation. 
The affected trees must be diligently 
sought out and cared for when 
detected. 

Great care must be taken to pre- 
vent the spread of any of these pests, 
and if that is done promptly the task 
of controlling them is not difficult. 

Other Varieties of Rubber Trees 

Some other species of rubber trees 
have been tried in these countries. 
For instance, . Castilloa had been un- 
der trial in Ceylon, the West Indies, 
and New Guinea, besides in the local- 
ities mentioned in our last chapter. 

The Mannihot has been tried and is 
still being worked to some extent. As 
early as 1883. there were nearly a 
thousand acres of it under cultivation 
in Ceylon. The tapping is rather diffi- 
cult and it has not, therefore, met 
with any degree of favor from the 
planter. 

Funtumia has been tried on 
plantations in Africa as we have 
pointed out in a previous chapter. 



RUBBER MANUFACTURE 



Ficus elastica, a rubber tree native 
of Asia, has been planted in Java 
and Dutch East Indies but the yield 
of rubber is so small that in some in- 
stances they have been cut down and 
Hevea planted in their stead. 

There has been a lack of uniformity 
in plantation rubber in the past, and 
strange as it may seem it is the fault 
of the rubber manufacturers. The 
planters are anxious to produce the 
grade of rubber most in favor with 
the ultimate consumer, whose speci- 
fications have been so often changed 
that the plantation managers have 
been at a loss to know just what grade 
is going to suit the trade when they 
buy their next consignment. 

This condition brings to our atten- 
tion more forcefully the fact that 
the whole industry is still in the expe- 
rimental stage. 

Theiv are those today who are of 
the opinion that the plantations in 
the East are not going to be able to 
compete with the West in the future. 
Also tbat when the large acrease of 



planted rubber trees are matured and 
come into full production there will 
be so much crude rubber ou the mar- 
ket that it will not pay a return suffi- 
cient to justify the continuance of 
the industry. However that may be 
we know that condition is not bother- 
ing us at present. 

The labor condition is becoming a 
very serious question on these planta- 
tions. A great many of the laborers 
are imported from India and Java, to 
such an extent that these two gov- 
ernments are taking steps to stop tli:- 
emigration of their people. 

The native of the Malay State- is 
uot of much value in the industry. 
He is too proud and lazy to work un- 
der the direction of a superior. It 
some task is given him where he feels 
independent he will work fairly well. 

The Chinese have been brought to 
the plantation and they are somewhat 
of the same temperament with the ex- 
ception that they are more in- 
dustrious and soon come to value too 
hierhlv their services. 




Fig. -0 — Vicmi Drying ox a Plantation 



CHAPTER VI 



Discussion of Colloid; 



Rubber belongs to one of those com- 
plex systems of matter known as col- 
loids, which, because of their com- 
plexity, have been left comparatively 
untouched while the more promising 
rields were being worked. Recent 
years have seen a change in this at- 
titude, so that we are now in pos- 
session of theories which, although 
investigators differ in their inter- 
pretation, are very hopeful. 

We are no longer held back by 
Graham's view that " they (crystal- 
loids and colloids) appear like dif- 
ferent worlds of matter and give oc- 
casion to a corresponding division of 
the science of chemistry." Physical 
chemists are now unanimously agreed 
that crystalloids and colloids are not 
different kinds of matter, but are 
rather different states of matter — 
that the same may be obtained in the 
one state or the other depending upon 
the necessary physical conditions of 
homogeneity as opposed to hetero- 
geneity. We may therefore define 
colloid chemistry as that branch of 
the science having to do with hetero- 
geneous systems of small particles, 
globulets. films, etc. A brief outline 
of colloids is in order. 

For the colloid state at least two 
'liases must be present. That phase 
which is divided and distributed (the 
internal phase) is known as the Dis- 
persed Phase ; the external or con- 
tinuous phase as the Dispersing 
Medium. We may therefore postu- 
late eight simple types of colloidal 
solutions, namely : 

Dispersing Dispersed 

iledti/m. Phase. Example. 

Gas Gas Impossible, since 

all gases are 
miscible in all 
proportions. 

Gas Liquid Clonds. mist. 

'las Solid Smoke, dust. 

Liquid Gas Foam. 

Liquid Liquid Emulsions. 

Liquid Solid Suspensions. 

Solid Gas Pumice. 

Solid Liquid Some gels. 

Solid Solid Allovs~ 



Broivniaii Movements 

Let us take a simple case of sus- 
pension. If we throw a stone into 
the water it sinks rapidly; broken 
up it sinks less rapidly. This has 
led to a statement that the rate of 
sinking is dependent upon the size 
of the particles, which is only true 
to a certain point. If we go far 
enough in our subdivision Ave come 
to the point where the Brownian 
movements in the suspension are 
stable indefinitely, if other conditions 
which will be explained later are sat- 
isfactory. The Brownian movements, 
so called because of their discovery 
by R. Brown in 1826 (Phila. Mag. 4, 
101, 1826), are just noticeable in 
particles about 0.01 mm. in diameter. 
Their nature may be readily observed 
by stirring a very little of an in- 
soluble fine organic powder, for ex- 
ample, carmine, with water and 
examining under a microscope. The 
larger particles will be seen to have 
a fairly regular oscillatory motion, 
while the finer particles take a more 
zig-zag course. Zsigmondy (Zur 
Erkefttniss der Kolloide, page 107) 
gives the following figures for the 
amplitudes of these oscillations for 
oold hvdrosols : 



(Of course, the amplitude and 
velocity vary inversely with the vis- 
cosity of the dispersing medium.) 

These Brownian movements are 
usually explained by the kinetic 
theorv first advanced by Ramsev 
(CJiem. News 65, 30. 1892), or some 
modification, as being due to the 
bombardment of the particles in sus- 
pension by kinetic vibration of the 
molecides of the medium. This ex- 
planation implies that all the energy 
possessed by the particles is derived 



38 



RUBBER MANUFACTURE 



from the medium: on the other hand, 
there is good reason to believe that 
it may. at least in part, he due to in- 
trinsic energy of the particles them- 
selves. 

Characteristics of Sols 

Colloidal solutions are distinguished 
from what we ordinarily recognize as 
true solutions by the following char- 
acteristics : 

1 — Osmotic pressure negligible. 

2 — Diffusion negligible. 

3 — Conductivity of medium un- 
changed. 

i — Elevation of the boiling point 
not measurable. 

5 — Depression of the freezing point 
not measurable. 

6 — Peptized or pectized by various 
salts, ions, electrical charges, etc. 
Graham suggested the use of the 
word peptonize, which because of its 
use in biology has been changed to 
peptize to indicate the change from 
gel to sol and peetize to indicate the 
reverse change.) 

7 — Optical characteristics showing 
distinct heterogeneity. 

The question of whether or not col- 
loidal solutions differ from true or 
molecularly dispersed solutions only 
in the size of the molecule has been 
much debated. The writer feels that 
the difference of opinion simmers 
down to the interpretation of per- 
sonal mental picture rather than any 
real difference in constitution. On 
the one hand, there are some who con- 
ceive a particle as made up of a group 
of molecules held together by un- 
known physical forces, probably the 
same as, or analogous to. electrical 
forces : on the other hand, others con- 
ceive the particle as a molecule held 
together by much the same forces as 
are the various atoms which in turn 
are much the same as. or analogous 
to. electrical forces. The latter ex- 
plains the low osmotic pressure and 
non-diffusion by the size of the par- 
ticles, the low conductivity, and the 
little influence on boiling or freezing 
points to the relatively small number 
of molecules in a given volume of the 
solution. 




Fig. 30 — Olive-Oil — Watee Emulsion 
Viscosity Cubve 

The former points to examples such 
as soap ; in water, the various char- 
acteristics of true solutions may be 
slightly observable due to alkali pres- 
ent either free or as the result of 
hydrolysis, but they are negligible ; 
on the other hand, alcohol solutions 
of soap behave perfectly normally in 
every respect. 

Still another case is that of olive 
oil-water emulsions. Starting with 
either as external phase, there is a 
fairly gradual increase in viscosity 
until we get to about 80 per cent 
olive oil and 20 per cent water, at 
which point the viscosity increases 
abruptly until it reaches a very high 
point. This may be explained by a 
chemical combination of olive oil with 
water at this point. Looking at it 
from the purely physical side, why 
should not the two combine when 
the other is in excess and give a 
smooth curve ? Explaining, can we 
not conceive of putting globulets of 
oil in water or water in oil until the 
point is reached where the external 
phase is not sufficient in volume to- 
reach around the internal phase and 
a rupture must take place, the 
medium constituting external force 
to become the internal phase or vice 
versa ! The force required to neu- 
tralize the surface tension of the ex- 
ternal phase and produce the rupture 
would be amply sufficient to account 
for the abnormality in viscosity. 

Surface Tension 

The condition of heterogeneity im- 
plies surface at the interface. The 
writer has found the following mental 
picture very helpful in the interpreta- 
tion of the phenomena. 

T\*e learned in our study of physics 



DISCUSSION OF COLLOIDS 



that every body of matter attracted 
every other body ; this applies to the 
smallest particle, even to the atom. 
The extent of this attraction is repre- 
sented by the formula, 

knii m 3 

f~ 
where 
F is the attractive force, 
m, and m„_ the mass of the respective 

bodies, 
r the distance separating the bodies, 
k is the constant. 

Because the mass of the earth is so 
great and we are so accustomed to in- 
terpret it in terms of bodies separated 
by microscopic rather than submicro- 
scopic distances we are apt not to 
appreciate its true significance unless 
it is called to our attention. Upon 
inspection, however, it is realized that 
as r becomes extremely small, even 
though the mass of respective bodies 
is very small, the extent of this force 
may become very great indeed, even 
approaching infinity as r approaches 
zero, which it probably does not do 
even on the interior of the atoms 
themselves. This force may well be 
the force which holds bodies together ; 
indeed, it may well be the source of 
chemical valence. 

The distance through which this 
for-ce may operate is very indefinite, 
but the sphere limiting its radius of 
action is at least larger than the par- 
ticle itself. Other particles within 
the sphere of attraction affect it and 
are affected by it; those outside do 
not. Let us then single out a mole- 
cule in the interior of a liquid. It 
exerts a sphere of attraction equal 
in all directions. (In speaking of 
this sphere of attraction, we do not 
necessarily wish to imply a perfect 
sphere. If the molecule happens to 
be a chain structure, the sphere 
would follow the general contour of 
the chain.) "Within this sphere there 
will be other molecules, approximate- 
ly an equal number in all directions, 
which in turn build up another 
sphere, and so on until we go beyond 
the surface. A molecule at the cen- 
ter therefore has the same counter- 
balancing attractions from all direc- 
tions and the net force tending to dis- 



place it is consequently zero, causing 
equilibrium in the molecule. 

These series of concentric spheres 
are thus continued until we reach the 
surface. The molecule on the surface 
has many molecules within the sphere 
of attraction on the interior, but rel- 
atively few on the exterior. It is 
consequently attracted to the interior 
very strongly without counterbal- 
ancing attraction from the exterior. 
The result is a high inward pressure. 
Just as a high outward pressure must 
be restrained by a high tension on 
the container walls, this inward 
pressure must result in a high sur- 
face compression in the surface film, 
which tends to cause the liquid to 
decrease in volume. This surface 
compression is incorrectly known as 
surface tension, and may be observed 
when we " heap " a spoon with 
liquid, or float a needle on the sui*- 
face of water, provided it is laid down 
carefiilly. 

Any increase in surface is attended 
by an increase of free energy at the 
surface; conversely, decrease in sur- 
face results in a decrease of free 
energy. Disintegration, evaporation, 
etc., require energy; agglomeration, 
condensation, etc., give up energy and 
are spontaneous. Large drops and 
crystals grow at the expense of 
smaller ones. 

We have no adequate means of 
measuring surface tension. It may, 
however, be considered in connection 
with osmotic pressure, which, if it 
acts in any manner similar to gas 
pressure, must require a restraining 
force. What other force than this 
surface tension can there be? And 
since the osmotic pressure is outward, 
there should be a lessening of the 
pressure inward causing the volume 
of the solution to be greater than 
the volume of solvent, which always 
happens. In the case of some solu- 
tions, the osmotic pressure is con- 
siderable ; the surface tension must 
therefore be even greater. 

Willard Gibbs pointed out the ob- 
vious result of these forces; namely, 
that there is no definite boundary 
at which the one phase leaves off and 
the other begins. True, the zone be- 
tween that which is distinctly com- 



RUBBER MANUFACTURE 



posed of the one phase and that which 
is distinctly composed of the other 
phase may be very slight; neverthe- 
less there is that zone at every inter- 
face where the two phases inter- 
mingle, and where surface forces 
come into play. The greater the sur- 
face tension the thinner the zone, i. e., 
the less chance to intermingle ; whence 
it will be seen that anything which 
tends to decrease the difference in 
surface tension between two immisci- 
ble phases will cause them to mix 
more readily; the converse is likewise 
true. This is of great importance in 
the selection and use of protective 
colloids. Surface energy equals speci- 
fic surface times surface tension. 

From the picture drawn, it is evi- 
dent that the center of the liquid is 
under greatest pressure. In the case 
of true or molecularly dispersed solu- 
tions, the concentration should be 
greater at the center, as is found to 
be the case with, for example, most 
inorganic salts. On the other hand, 
where the solution is only apparent 
(i. e., heterogeneity), as, for example, 
soap in water, there will be a 
greater concentration of the solution 
at the surface. Increase in surface 
concentration will result in decrease 
in surface tension and vice versa. 
Where we have this difference in con- 
centration between the surface and 
the interior, we have Avhat is known 
as adsorbtion. If the surface con- 
centration is in excess, as is usually 
the case, we have positive adsorbtion. 
1 1' such a solution is shaken with a 
very fine powder giving a very large 
surface (size of particles is not neces- 
sarily a criterion, since, as in the 
case of various blacks, the material 
may be spongy and thus present an 
enormous amount of surface in the 
capillary pores) nearly all of the solu- 
tion may be removed from the sol- 
vent. Surface deficit must necessari- 
ly be very slight, since the limit must 
necessarily be pure solvent in the sur- 
face, which would give rise to nega- 
tive adsorbtion ; indeed, even this case 
may be regarded as positive adsorb- 
tion of the solvent. 

Adsorbtion comes to an equilibrium. 
Thus, if a^ given volume of solution 
of certain concentration is shaken 



with a weighed amount of adsorbant 
until equilibrium is reached and is 
then diluted, the final concentration 
of the solution will be* the same as 
if the dilution had been made before 
starting. This gives rise to the ad- 
sorbtion equation. 

x 1 

— = k e - 
m n 

where 

x is the weight of substance ad- 
sorbed, 
m the weight of adsorbant, 
e the volume of the concentration 
after equilibrium, 

h and - are constants. 
n 

The question as to whether adsorb- 
tion is chemical or purely physical 
combination has been much debated. 
Indeed, the discussion simmers down 
to a matter of viewpoint. It seems 
highly probable that both forces are 
akin to electrical attraction and there- 
fore may easily be the same. 

Catophoresis and Electro-endosmos 

In no place does the phenomenon 
produced by electrical charge play 
a more important role. At the inter- 
face between two phases there is al- 
ways a potential difference. If a 
liquid, say water, is placed in two 
vessels connected by a capillary tube 
and subjected to electrolysis it will 
flow with the current ; if finely 
divided particles of an insoluble pow- 
der such as metal, sand, etc., be sus- 
pended in the liquid, it will move in- 
stead. This phenomenon is known as 
cataphoresis. If the flow is through 
a semi-permeable membrane, it is 
known as electro-endosmos. There 
are three cases possible. 

1 — The particles are poor con- 
ductors and have slight tendency to 
coalesce. Such particles will move 
sluggishly toward the electrode and 
will congregate around it. Those 
actually coming in contact with the 
electrode will deposit a part of their 
charge, but not all of it; the others, 
being such poor conductors as not to 
be able to transfer their charge, will 
retain it, and when the current stops 
will mutually repel each other as far 
as possible, thus diffusing themselves 



DISCUSSION OF COLLOIDS 



41 



throughout the liquid substantially 
as before being subjected to the in- 
fraence. 

2 — Particles which are good con- 
ductors but have little tendency to 
•coalesce will move up to the electrode, 
get rid of their charge and take on 
•one of opposite sign, after which they 
will start for the other electrode. 

3 — Particles which are good con- 
ductors with a tendency to coalesce 
will move up to the electrode, dis- 
charge, and be precipitated. 

We have discussed the individual 
conditions which bear upon colloidal 
phenomena. We see that colloids are 
systems consisting of at least two dis- 
tincJj heterogeneous phases, one of 
which is extremely finely divided and 
•dispersed in the other and which is 
more or less affected by Brownian 
movements, depending upon the vis- 
cosity of the dispersing medium. This 
fine state of division gives rise to an 
■enormous extent of surface interface, 
which, beeatise of its nature, gives a 
•correspondingly large amount of free 
energy in form of surface energy and 
electrical energy. The activity of 
this energy probably contributes the 
Brownian movements and, in being 
neutralized, gives rise to adsorbtion. 
We can postulate the behavior of so- 
lutions, that is, the conditions of pep- 
tization and pectization. 

Since the formation of a large 
amount of surface involves an enor- 
mous amount of free energy which 
is neutralized in part bj r adsorbtion, 
we have a basis for Freundlich's as- 
sertion (Eapilarchemie 52, 154. 1909) 
that adsorbtion tends to lower the 
surface tension of the adsorbing 
phase, from which it follows that any 
substance which is adsorbed by an- 
other tends to disintegrate and pep- 
tize the latter. In making this state- 
ment, however, we must bear in mind 
that, since adsorbtion depends on the 
surface and disintegration depends 
upon the cohesion between the par- 
ticles, there may be no apparent con- 
nection between the two. Thus the 
same mass of porous material is much 
more easily disintegrated than if it 
occurs in a more dense form. 

Bancroft {Jour. Phys. Chem. 20. 
85, 1916) has discussed this subject 



in detail. He says: " We may have 
peptization by a solvent, by a dis- 
solved non-electrolyte, by an ion, by 
an undissociated salt, by a colloid. ' ' 

As we raise the temperature, ad- 
sorbtion decreases, but the cohesion 
between the particles also decreases; 
thus glass, coagulated albumin, etc., 
are peptized by water, provided the 
temperature is raised to a point where 
the cohesion between the particles is 
sufficiently small to be exceeded by 
the tendency to absorb the solvent. 

One of the many examples cited 
in the case of a dissolved non-elec- 
trolyte is the action of sugar in pre- 
venting the precipitation of ferric 
hydrate when ferric chloride is treated 
with ammonia. 



Fig. 31 — Iox Cckve 

The action of ions is closely asso- 
ciated with their supposed electrical 
nature. If we add a small amount 
of an electrolyte to a solution, preci- 
pitation takes place. Ions carrying 
a charge opposite in sign to the dis- 
persed phase are adsorbed more rap- 
idly, thereby neutralizing the charge 
which keeps them apart. Very soon 
the place is reached where the charge 
which keeps the particles apart is neu- 
tralized, and instability results. Be- 
yond this point, the adsorbtion of 
the first ion varies but slightly with 
increase in concentration, but the ad- 
sorbtion of the ion of opposite charge 
increases until we get a correspond- 
ing excess of the opposite charge and 
consequent peptization by the salt. 
In general, the action of ions follows 
Schultz's law that the higher the 
valence the greater the influence of 
a single ion. This rule is disturbed, 
however, by the preferential adsorb- 
tion of certain ions. 



42 



RUBBER MANUFACTURE 



The examples of peptization by a 
colloid are without number in our 
every-day experiences. We have to 
go no further than the use of soap 
for washing; the insoluble dirt ad- 
sorbs the soap film and is peptized 
by it, after which it can be easily 
washed away. 

It is not the purpose of this work 
to go into the study of colloids. In 
giving this discussion, the writer has 



merely attempted an explanation of 
some of the fundamental principles 
underlying the behavior of colloids 
so that their influence 'on the rubber 
colloid may be appreciated. Students 
are earnestly requested to study some 
of the text books and numerous arti- 
cles on colloids, as well as the applica- 
tion of the principles to other in- 
dustries, such as the cellulose, glue, 
and tanning industries. 



CHAPTER VII 



Colloidal Action of Crude Rubber and Its Application in Rubber 
Manufacture 



The latex as it comes from the tree 
is a milky white fluid which in the 
light of colloidal chemistry should be 
clashed as an emulsoid in contrast to 
a suspensoid ; namely, a heterogeneous 
system consisting of two distinct 
liquid phases. The dispersing 
medium is water and the dispersed 
phase consists of globules of ca-. 
outchouc ranging in size from 1/u to 
2/i. This emulsion is made fairly 
stable by the presence of certain 
resins, albuminoids, proteids, sugars, 
mineral salts, etc., which act as pro- 
tective colloids. 

This latex upon examination shows 
pronounced Brownian movements. 
As is the case in nearly all hydrosols, 
the dispersed phase bears a negative 
charge as is shown when the hydrosol 
is subjected to electrolysis, when the 
globules migrate 1o the anode region. 
From this behavior, we may postu- 
late that upon the addition of a 
kation, these globules will tend to be 
precipitated while the addition of 
anions will tend to make the emulsion 
more stable. 

It is quite possible that the 
caoutchouc itself in the latex is posi- 
tively changed, but that it has ad- 
sorbed enough of the protective col- 
loids which are negatively charged to 
more than balance the positive effect 
and thus give to the globule the effect 
of being negatively charged. 

Therefore anything winch tends to 
destroy this protective colloid, tends 
to destroy the negative charge which 
gives stability to the emulsion. 

Let us now turn our attention to a 
discussion of the manner in which 
these principles are applied in the 
crude rubber industrv. 



Preservation oj Latex 

First let us consider the preserva- 
tion of the latex where it is not de- 
sired to coagulate it immediately. We 
find the general practice is to add 
ammonia. This was first done with- 
out the knowledge of any scientific 
reason as a basis for it ; now, however, 
it. may be explained by the principle 
which we have just mentioned. The 
ammonia introduces hydroxyl ions, 
bearing negative charges and these 
tend to increase the potential dif- 
ference between the two phases and 
thus increase the stability of the 
emulsion. 

Next, we shall endeavor to show 
how these principles are applied in 
the coagulation of latex. To do this 
we shall divide the different means of 
coagulation into the divisions : 1 — 
Mechanical ; 2 — Electrolytic ; 3 — 
Dilution; 4 — Natural; 5— Heat with- 
out evaporation; 6 — Heat with 
evaporation ; 7 — Chemicals. 

Tn the mechanical coagulation of 
rubber, we simply take advantage of 
the fact that in the latex there are 
two distinct phases of different 
density. Therefore by centrifnging 
the latex, we are able to effect a 
separation. Rubber obtained by this 
method compares favorably with the 
rubber obtained by other means, but 
the process is a tedious one and rather 
expensive also. 

The electrolytic method is one of 
theoretical interest only. As the latex 
is such a poor conductor of electri- 
city, and the globules simply collect 
in the region of the anode, unless the 
voltage is very high those in actual 
contact with the anode will be the 



RUBBER MANUFACTURE 



only ones which will discharge and 
thus precipitate. 

Coagulation by dilution in a great 
many cases produces unfortunate 
results, while again it is used 
to advantage. The necessity of 
collecting latex out in the open 
in a region where the precipitation 
is so abundant makes dilution of 
the latex by rain water inevitable 
at times. Such latex coagulates in 
much the same fashion as cream sep- 
arates from milk which has been di- 
luted. Then in the case of cup wash- 
ings, the latex which has been 
washed out from the cups is 
saved. On a few small plantations 
where the quality is not a considera- 
tion, and in places where better meth- 
ods are unknown, this method is used 
as a regular procedure. The reason 
for the precipitation undoubtedly lies 
in the fact that the protective colloids 
are more or less soluble in the in- 
creased volume of the dispersing 
medium. When these protective col- 
loids are removed, it results in the pre- 
cipitation of rubber. While compara- 
tively little is known as to why cer- 
tain of these materials which make up 
protective colloids are essential, it is 
a fact that their absence results in an 
inferior product. Consequently this 
method is by no means satisfactory 
and is not employed where its use may 
be avoided. 

When the latex is allowed to stand 
for some time, it will. coagulate spon- 
taneously. This is no doubt due 
to the formation of acid in - the latex 
from causes which will be discussed in 
a later chapter. The acids which are 
produced furnish the necessary hydro- 
gen ions to cause the coagulation of 
the rubber. Due to the fact that the 
conditions cannot be or are not regu- 
lated correctly, an inferior product 
invariably results. 

If the latex is subjected to heat 
without evaporation, we have a com- 
bination of results similar to dilution, 
that is increased solubility of protec- 
tive colloids, and the formation of 
acids as in natural coagulation! which 
is probably still further complicated 
by hydrolysis. This method of coagu- 
lation i^ of little practical importance. 

When the latex is evaporated by 
addition of heat, coagulation results. 



There we have much the same condi- 
tions as in the ease of heating without 
evaporation, that is in the formation 
of acids and hydrolysis but we have 
in this method the advantage of uni- 
form conditions such as temperature, 
time, and also the fact that the pro- 
tective colloids which are soluble can- 
not be removed from the rubber. 
Usually, too, in the case of South Am-' 
erican rubbers, the process is carried 
on in the presence of smoke which 
contains various acids and alcohols. 
These tend to facilitate the coagula- 
tion and at the same time inhibit the 
development of bacteria. 

The foregoing methods are all 
primitive and whatever merits they 
may possess are accidental. 

Coagulation by Chemicals 

By all means the most important is 
the coagulation effected by chemicals. 
The ones in most common use may be 
classified under the following heads: 
Acids, salts, alcohols and ketones. 

We would naturally expect all acids 
to have a coagulating effect in propor- 
tion to their degree of ionic dissocia- 
tion since they owe their power of 
coagulation to the concentration of 
hydrogen ions. The question of selec- 
tive adsorbtion plays no role in this 
because the hydrogen ions are the 
same regardless of their source. 
Strong acids should therefore be bet- 
— fcer coagulants than weak acids since 
they possess a higher degree of dis- 
sociation. Therefore we should ex- 
pect to find the highest dissociated 
acids being used for the above pur- 
pose. These are muriatic, nitric, and 
sulphuric acids. In actual practice, 
however, the first two are not permis- 
sible. 

Muriatic acid, while it has the de- 
sired coagulating effect, also has a 
deleterious effect upon the rubber. 
This might be explained upon the 
ground that as a halogen acid, it acts 
upon the polyperene molecule at the 
double bonds thus tending to form ad- 
dition products. 

Nitric acid also possesses a marked 
degree of coagulation but here the 
strong oxidizing power of the acid 
renders it useless. Sulphuric acid. 
however, is used quite extensively as 
it possesses neither of the objections 
which characterize the other two. 



COLLOIDAL ACTION OF CRUDE RUBBER 



The question naturally arises, why 
should acetic acid be used in prefer- 
ence to sulphuric ? ' It must be borne 
in mind that acetic, however, is by far 
the strongest or most highly dissoci- 
ated of the so called weak acids. It 
furnishes, therefore, the necessary 
concentration of hydrogen ions very 
nearly as readily as the sulphuric 
acid. All of either acid must be com- 
pletely removed from the coagulum. 
Sulphuric acid must be entirely re- 
moved by washing, and to remove it 
completely requires prolonged wash- 
ing, which experience has shown im- 
pairs the rubber. With acetic acid, 
on the other hand, it matters not 
whether all the acid is removed by 
washing- since any that remains will 
be volatilized and thereby removed in 
the process of drying. 

The other organic acids have the 
two objections, first, that they are too 
feebly ionized and secondly, that their 
cost makes them prohibitive. 

Under salts, those most commonly 
used are sodium chloride, alum and 
soap. 

If we apply the law of Schulze, that 
is, that the higher the valency of the 
kations in a hydrosol, the greater will 
be its precipitating power, then we 
should use those salts which not only 
furnish a high concentration of 
kation but also those which possess a 
large valence. Of course, this condi- 
tion may be disturbed by selective ad- 
sorbtion. 

We find sodium chloride is used 
only where the more primitive meth- 
ods are in vogue. It is an extremely 
common substance and eousequently 
was available for primitive experi- 
ments. It accidentally possessed the 
property of being highly dissociated. 
having the necessary number of 
kations to make it effective as a coagu- 
lant. On the other hand, where more 
scientific methods of reasoning have 
been brought to bear, we find alum is 
used more or less extensively. Then 
we get a much higher electrical charge 
with a small number of ions. Soap 
lias found little application as would 
naturally follow from what has been 
stated above, namely : it possesses a 
very low degree of ionization and a 
low charge on the kation. 



The use of salts is in no case de- 
sirable because if any remain in the 
rubber they will undoubtedly under- 
go hydrolysis and the resulting prod- 
ucts are likely to be detrimental to 
the rubber. Their complete removal 
is almost impossible even with exces- 
sive washing. 

In the use of alcohols and ketones 
coagulation is effected, no doubt, 
because these substances have the 
power to dissolve the protective col- 
loids and thus allow the rubber glob- 
ules to coalesce. It is said that a 
much better grade of rubber results 
when either ethyl alcohol or acetone 
is employed ; this being no doubt due 
to the fact that undesirable substances 
are dissolved out while the more de- 
sirable ones remain in the rubber. 

In the case of Guayule, we are con- 
fronted by a special proposition. This, 
coming as it does from the shrubs, can- 
not be obtained by the ordinary means 
of tapping. The process is largely a 
mechanical one, but the principles of 
peptization and pectization are both 
taken advantage of in this process. 
The shrubs are macerated in pebbh 
mills and then digested with an alka- 
line solution. This pectizes the rub- 
ber and makes it possible to remove it- 
After this it is precipitated. The pro- 
cess is largely secret. 

Application of Colloidal Chemistry 

Next in order we shall discuss ;r 
few of the applications of colloidal 
chemistry to rubber manufacture. 

Considering mixing, we must first 
call attention to the fact that in break- 
ing down the rubber on the mixing 
mills, we increase the surface. Inas- 
much as the colloidal . action of the- 
rubber does play a part in its be- 
havior, the extent to which we in- 
crease the surface by this breaking 
down process will have a proportion- 
ate effect \rpon this action. 

Among our compounding ingredi- 
ents we have some materials which 
have high adsorbtive power, others, 
which are comparatively inert, and 
still others- which are more or less ad- 
sorbed. Consequently we may expect 
a difference in the behavior of the 
stock depending upon the order in 
which the compounding ingredients 



4o 



RUBBER MANUFACTURE 



are added. For example, let us take 
a compound containing rubber and 
sulphur, a highly adsorbtive material, 
and a material capable of being easily 
adsorbed. If the easily adsorbed 
material is one that directly affects 
the rubber itself, the probabilities are 
that it should be added first in order 
that the full extent of the adsorbtive 
forces between it and the rubber may 
be realized. If. on the contrary, the 
highly adsorbtive material has been 
added first, it would have no doubt 
adsorbed the rubber and thus satisfied 
or at least materially lessened the ad- 
sorbtive force which the rubber pos- 
sessed. 

It may be noted in passing that 
there are a few materials which have 
a great influence upon the physical 
properties of the cured compounds 
where they are used: and these sub- 
stances have a high adsorbtive power. 
As the most notable examples of this 
phenomenon we may mention zinc 
oxide and lamp black. The latter is 
one of the best adsorbents known and 
has the property of increasing tensile 
strength of rubber compounds more 
than any other substance. Without 
exception the materials used in rub- 
ber compounding which have slight 
adsorbtive power are practically 
inert and serve merely as fillers. 

Of course we must not fail to re- 
member that these materials which 
we have mentioned which have a great 
absorbtine power, likewise possess au 
enormous surface due to their fine 
state of division and their porosity. 
On the other hand, the others are com- 
paratively coarse and more compact. 

The theory has been advanced and 
has received considerable support that 



the swelling of rubber in benzene may 
be accounted for as follows: The 
rubber possesses a more or less cellu- 
lar structure. Therefore, when it is 
placed in benzene, the solvent enters 
these cells and adsorbs certain sub- 
stances therein and thus produces 
osmotic pressure, which distends the 
individual cells untfl they burst open 
and then disperse through the solu- 
tion. If this theory is correct, it nat- 
urally follows that when the solvent 
is evaporated, the residue should 
possess different properties than the 
original rubber. TVe know that this 
is not true. 

A much more reasonable explana- 
tion may be found in our theory of 
peptonization advanced in the last 
chapter. From this we would explain 
the phenomenon of rubber solution as 
follows : 

"When rubber is placed in the sol- 
vent, the latter is adsorbed by the rub- 
ber. The volume of the solvent ad- 
sorbed causes the swelling of the rub- 
ber until finally sufficient lias been ad- 
sorbed to break up the cohesion be- 
tween the rubber particles and dis- 
perses it through the entire solution. 
VThen such a solution is evaporated, 
the particles remain unruptured and 
will finally go back to their original 
state. This is more in accordance 
with what actually happens. 

Furthermore, if the rubber has been 
first broken down upon the mill, and 
thus its surface increased, it will ad- 
sorb the solvent more easily and give 
a solution in a shorter time. 

The role of colloidal phenomenon, 
as it is applied to vulcanization and 
to reclaiming will be considered in the 
following chapters. 



CHAPTER VIII 
Different Means of Coagulation 



"While discussing the different va- 
rieties of rubber which come from 
the various sources, we have called 
attention in each case to the methods 
used in their coagulation. Some of 
these have been primitive and most 
have lacked a scientific basis. The 
resuTl of this has been that some rub- 
bers from certain localities have been 
very good and uniform while those 
from other places are characterized 
by lack of uniformity, and therefore 
are expensive experiments most of the 
time. 

Of course, at present, the methods 
of control are more luiifomi on the 
plantation and as a result the rub- 
ber from these sources is the most uni- 
form found in the market. That leads 
us to suspect that the wide variance 
in native rubbers is occasioned prin- 
cipally by the lack of uniform meth- 
ods of coagulation. This has led 
men to investigate the different 
methods in use, with the idea of try- 
ing to find some more satisfactory 
process than is at present known. 
They have been guided by observa- 
tions of conditions which exist in 
places from which the various grades 
are obtained. 

We know the rubber from the Ama- 
zon to be the most uniform of any 
wild rubber on the market. When 
we observe the methods by means of 
which the seringueiro collects and 
coagulates the latex from the Hevea 
and thus obtains Para rubber, we 
come to the conclusion that the 
process wherever and by whomever 
used is one that will produce a uni- 
form product. On the other hand, 
when we observe the product from 
Africa and notice the great differ- 
ences even in the same grades, we 
are satisfied in our own minds that 
the methods used must be at fault. 



The whole trade recognizes that we 
have not at present any method of 
coagulation that is entirely satisfac- 
tory. This is very apparent when 
we realize that even the method 
which produces the most uniform 
rubber of all, namely, the plantation, 
is at present under severe criticism, 
and chemists are employed to make 
a thorough study of this whole ques- 
tion in order to substitute a better 
one. 

This study is based upon certain 
principles of colloidal chemistry and 
it is hoped that by the aid of these 
investigations we are going to be able 
to bring forth something new and 
better. We know that the stability 
of latex from different sources varies, 
and we have come to the conclusion 
that this is due to the different size 
of particles in the different emulsions, 
to the electrical charge, and to the 
presence of protective colloids, etc. 
Fickendey {Z. Chem. hid. Kolloids, 
1911, 8, 43) calls attention to the fact 
that coagulation in general consists 
in the removing of the proteins or 
peptones, which serve as protective 
colloids, and then the neutralization 
of the electrical charges. Upon the 
addition of acid to the latex, we ef- 
fect coagulation in all cases except 
Funtumia. This latter fact has been 
explained upon the ground that it is 
a case of a peptone acting as the 
protective colloid instead of a pro- 
tein. However, Spence has shown 
that the size of the particle in the 
Funtumia latex has a great deal to 
do with its stability also, for he re- 
moved the peptone by treatment with 
trypsin and no coagulation resulted. 
(Quar. Jour. Reprints, 1907, 9, 5.) 

The Brownian Movements are ap- 
parent in the latex and V. Henri 
(Le Caoutchouc et la Gutta Percha, 



47 



RUBBER MANUFACTURE 



3 . o. 2405) took advantage of this 
to study the effects of acids and 
alkalis upon it. He found that the 
addition of acids greatly reduced the 
velocity of the rubber particles, while 
alkalis had much less effect. "When 
the acid was increased, the particles 
seemed to form in a sort of network. 

This is interesting from a scientific 
point of view, but its influence upon 
the manufacture may be slight, yet 
today we are also having it studied 
from the manufacturer's side. 

It was to study this problem from 
this angle that Eaton and Grantham, 
in the Department of Agriculture of 
the Federated Malay States, started 
on what might be called the first 
scientific investigation of this subject 
of coagulation and its effect upon 
the rubber obtained for manufactur- 
ing purposes. 

The manufacturer had observed 
the difference, which we find in the 
mechanical curing of rubber from 
different sources and in fact from 
the same source. Some forms of 
rubber from a certain plantation will 
cure in a way different from that of 
another variety from the same place. 

Corresponding grades from different 
plantations likewise show different 
peculiarities in curing. This of 
course raised the question as to what 
caused this variance. It led some 
men to think that in order to use 
any rubber intelligently, one must 
know the complete life history of it: 
where it came from, how it was gath- 
ered, how it was coagulated, how it 
was treated after coagulation, what 
form it was put into, how old it was. 
and many more facts. 

In the first experiment of Eaton 
and Grantham, which appeared in 
the Agricultural Bulletin of the 
F. M. S. 3 they call attention to two 
facts. 

(1) That in plantation rubbers 
there is a great variation, but this 
comes largely in the rate of cure and 
not in mechanical properties, since 
similar mechanical properties can be 
obtained in the vulcanized material, 
provided the correct rate of cure of 
the rubber under specific conditions 
is known. 



2 That this variation in rate of 
cure or vulcanizing capacity is due 
to some substance existing in the 
latex, or formed subsequently, which 
in the prepared raw rubber acts eata- 
litically as an accelerator, and that 
the rate of cure of raw rubber de- 
pends on the amount of this substance 
remaining in the raw rubber, which 
again depends on the mode of coagu- 
lation and preparation. In trying 
to establish these, they selected what 
they regarded as a set of uniform 
conditions for determining what is- 
known as the "" optimum cure." that 
is. the cure which shows the maxi- 
mum product of elongation by tensile 
strength. They cured all of their 
samples at a temperature of 140 
C. and took test- strips every fifteen 
minutes. The sulphur content was 
10 per cent of the whole mixture. 

The first tests were made upon 
Plain Crepe and Smoked Sheet. Both 
of these showed the optimum cure at 
three hours. At this point they re- 
ceived a sample of *" Byrne cured 
slab. : ' and when this was tested out it 
showed the "' optimum cure "' at one 
hour and fifteen minutes. Here we 
have a rubber which cures an hour 
and forty-five minutes more quickly 
than plain or smoked sheets, and yet 
is obtained from the same latex. Tou 
may immediately realize what this 
means to the manufacturer of today. 
Here two questions presented them- 
selves : 1 TVas it due to the Byrne 
fumes, or 2 the form in which the 
rubber was prepared? They then 
prepared what is known as a Byrne 
Loaf i this is made by rolling sheets 
cured by the Byrne fumes around a 
stick, thus building up a solid cylin- 
der of superimposed sheets ; this 
rubber never completely dries in this 
form and has to be ereped and dried 
before vulcanizing. The results on 
this loaf, and also upon pressed sheet, 
showed the optimtun results at two 
hours and forty-five minutes. This is 
practically the same time as that re- 
quired for plain crepe or smoked 
sheet, and therefore points to the fact 
that it is not the Byrne fumes which 
cause the variation in the rate : 
cure. 

A sample was then prepared by- 



DIFFERENT MEANS OF COAGULATION 



coagulating the latex in thin layers 
in shallow pans in a smoke house 
and thus superimposing further lay- 
ers daily for a period of a week. By 
this method a slab of rubber result- 
ed, and when this was cured and 
tested it came to the optimum test 
in an hour and a half. In other 
words, a rapid curing rubber had 
been produced, and we are almost 
safe in saying from these two tests 
that the rate of cure is due to the 
form rather than to the fumes. 
Further tests revealed the fact that 
smoked sheets vulcanized more slowly 
than plain sheets, and hence the con- 
elusion that smoking has a tendency 
to retard the rate of cure. We may 
tflT>refore call attention to the follow- 
ing facts : 

(1) Slab rubber smoked by Byrne 
fumes or rubber coagulation by 
smoke, by superimposing layers of 
latex, cures much more rapidly than 
plain crepe or smoked sheet. 

(2) Unsnioked sheet cures more 
rapidly than smoked sheet or plain 
crepe. 

Latex was next placed in a large 
wooden box with movable partitions, 
so that all might receive the same 
treatment during coagulation: then 
from the coagulum the following 
samples were prepared: 

(a) Smoked sheet, which showed 
its '" optimum cure " in two hours 
and forty-five minutes. 

(b) Smoked sheet, creped when 
dry ; this required two hours and 
forty -five minutes. 

(c) Smoked slab, "optimum cure,'' 
one hour and forty-five minutes. 

{d) Unsnioked sheet, " optimum 
cure." two hours and forty-five 
minutes. 

(c) Unsnioked sheet, creped after 
drying. " optimum cure,'' two hours 
and forty-five minutes. 

(/) Unsnioked slab, " optimum 
cure," one hour. 

The conclusions to be drawn from 
these tests are that creping of dry 
sheet has no effect upon rate of vul- 
canization : also, that slab is the 
most rapid curing form of rubber : 
and lastly, that smoking will retard 
the rate of cure on slab. To explain 



this behavior, two theories present 
themselves : 

(1) That the latex contains, in 
addition to the caoutchouc, some con- 
stituents which influence the rate of 
cure of the rubber, this substance 
not being precipitated by ordin- 
ary coagulation. Consequently, the 
greater the quantity of serum remain- 
ing in the rubber, the greater will be 
the quantity of this substance present 
in the raw rubber. If this is the 
case, the effect of smoking is appar- 
ently the destruction of this sub- 
stance. 

(2) It may be, however, that this 
substance does not exist in the latex, 
but is formed from some constituent 
of the latter. In this case the reten- 
tion of the serum in the rubber would 
appear to encourage the formation 
of the catalytic substance. Our or- 
dinary methods of analysis of crude 
rubber, of course, will not reveal the 
presence of these substances. For 
instance, we determine the nitrogen 
in the rubber and calculate it all as 
proteins and this may be far from 
the actual truth of the way the nitro- 
gen really does exist. We do know 
that certain amines have an accelerat- 
ing effect upon vulcanization, and 
it follows that perhaps some of these 
proteins do decompose into amines, 
and therefore the greater the amount 
of serum left in the rubber, the 
greater will be this effect. To 
strengthen this theory, Eaton and' 
Grantham observed that we get slow 
curing rubbers from latex treated 
with preservatives, or from smoked 
rubbers, which act in the same way. 
If this change is caused by an enzyme, 
then the same may be expected for 
the preservative, or smoke would of 
course kill it and thus produce a slow 
vulcanizing rubber. 

That this material is present in the 
latex is also substantiated by the fact 
that synthetic rubber is very difficult 
to vulcanize. 

Another fact pointing in the same 
direction is that air-dried slab is the 
most rapid curing and also has the 
most serum remaining in the rubber. 

Fine hard Para is rather slow cur- 
ing, clue to the fact that the smoke 
in coagulating has its maximum ef- 



RUBBER MANUFACTURE 







Latex, 


TABLE I 

Acetic Acid Coagulated 
1 








1 
Slabs 






1 
Sheets 

1 




Smoked 




Unsmoked 
Air dried 

Creped 

1 

lhr. 


Smoked 




1 
Unsmoked 
Air dried 

1 


Creped 
1M hrs. 


I 1 
plain creped 

2% hrs. 2% hrs. 




1 
plain 

1 
2% hrs. 


1 
creped 

1 
2h hrs. 





Time Required foe Cubing Various Kinds of Rubbek. 



feet. The ' ' optimum, cure ' ' requires 
from two and one-half to two and 
three-quarters hours. 

The rate of cure of samples from 
different states shows quite a vari- ■ 
ance due to many causes, e. g., dilu- 
tion of latex, working of rubber, 
thickness of rubber, smoking, rapid- 
ity of drying, amount of coagulant, 
etc. (Agricultural Bulletin, Feder- 
ated Malay States, March, 1915.) 

The lack of uniformity in these 
rubbers is of great importance to the 
manufacturer, for if by regulating 
the preparation of the rubber from 
the latex we are able to procure a 
rapid curing rubber, then a great 
deal of cost in the manufacture is 
saved and a greater output is also 
made possible with the same equip- 
ment and number of men. 

Eaton and Grantham have also 
conducted experiments to find the ex- 
tent to which lack of uniformity in 
the mechanical method of procedure 
in the preparation of rubber from the 
latex caused variation in the product. 
(Agricultural Bulletin, Federated 
Malay States, 111, 218, 1915, et seq.) 
They found : 

(1) That after the rubber has once 
been reduced to a thin sheet, exces- 
sive creping has little or no effect. 

These conclusions were based upon 
the results obtained from passing 
different lots of the same rubber 
through the creping machine five, ten. 
fifteen, twenty, and twenty-five times, 
respectively. Excessive maceration, 
however, does seem to have a slightly 
retarding effect upon the rate of cure. 



An interesting feature of the experi- 
ment was shown by repeating the 
tests on mixtures out of these 
samples, made eight months later. 
These tests indicated somewhat 
slower cure in the sample creped 
twenty-five times. This is particularly 
interesting because of the apparent 
recovery, which has been so com- 
monly noticed after rubber broken 
down on the mills has been allowed 
to stand. 

(2) That the use of more acid than 
necessary to produce coagulation has 
the effect of slightly retarding the 
cure. The use of sodium bisulphite 
has no effect. 

(3) That samples of rubber from 
the same latex were taken at different 
stages in the preparation as follows : 
a, Coagulated slab and allowed to 
drain; b, after rolling once; c, rough 
crepe ; d, thick crepe ; e, thin crepe. 

These samples were kept for twenty 
days; then samples A, B and C were 
made into thin crepe and all five 
samples were dried, after which they 
were compounded similarly and 
cured. The " optimum cures " re- 
ported were: a, 1 hr., 30 min. : b, 2 
hr.; c, 2 hr., 30 min.; d, 2 hr., 45 
min. ; e, 3 hr., thus substantiating 
their contention that each step of the 
process seems to have a retarding in- 
fluence on the cure. 

Continuing on this line, they went 
further into the effect of drying in 
hot air driers up to 2 hr., at 150 
deg. F., samples being taken prac- 
tically as before and also a sample 
being taken from the drier every 



DIFFERENT MEANS OF COAGULATION 



hour. All of the . samples, which 
had been in the drier required 3 
hr., 15 min. for curing or 15 min. 
more than the time required for thin 
crepe. 

(4) That tests of the product from 
the estate handled by the same 
methods were quite uniform. One 
interesting thing was indicated 
through the course of these tests. On 
two occasions the trees were per- 
mitted to rest longer than usual be- 
cause of rain for a whole day ; on 
another the tapping was late. The 
quality of rubber obtained from 
these subsequent tappings was above 
th£ average. 

(5) That the following expei'iments 
indicated the effects of leaving the 
coagulatum in slab form for ten days 
before curing : 

a Block prepared as usual on the 
day following coagulation, cured in 
3 hr., 15 min. 

b Block prepared after leaving 
coagulum from some of the same latex 
in the slab form ten days before crep- 
ing, blocking and drying, cured in 
1 hr., 15 min. 

c Slab, prepared the same as B, 
cured in 1 hr., 15 min. 

Sodium bisulphite had no effect 
when used in parallel experiments. 
The mechanical qualities of a were 
also inferior. 

By mixing proportionate amounts 
of fast and slow curing rubbers to- 
gether, the rate of cure may be ad- 
justed to uniformity. They explain 
the uniformity of fine hard Para by 
the fact that a single ball represents 
latex collected day after day for a 
period of months. In passing, it is 
but fitting to note that many com- 
pounders prefer to use a mixture of 
rubbers in their stocks so that the 
variation in different lots of each may 
be averaged and a more uniform 
product obtained. 

An attempt has also been made 
(Agricultural Bulletin, Federated 
Malay States, IV, 1, 1915) under 
the direction of Mr. Eaton to deter- 
mine the influence of the nitrogen 
content on the cure with the possible 
view of regulating this factor to the 



best advantages. Their data may be 
summarized as follows : 

Type of Rubber Ns Cure 

Smoked sheets 0.445 per cent 3 hr. 

Smoked sheets after creping. . . 0.441 per cent 3 hr. 

Smoked slab after creping 0.451 per cent \% hr. 

Unsmoked sheet 0.423 per cent 2 jj hr. 

Unsmoked sheet after creping. . 0.434 per cent 2% hr. 

Unsmoked slab after creping.... 0.321 per cent 1}£ hr. 

Thick smoked slab 0.425 per cent lji hr. 

Thin smoked slab 0.39S per cent 1 Jf hr. 

Thick smoked sheet 0.400 per cent 2% hr. 

Thin smoked sheet 0.416 per cent 3 hr. 

Thick unsmoked slab 0.210percent l^hr. 

Thin unsmoked slab 0.352 per cent IK hr. 

Thick unsmoked sheet 0.3S6 per cent 2}4 hr. 

Thin unsmoked sheet 0.394 per cent 3 hr. 

Unsmoked slab dried externally, 

results calculated on S2.7 per 

cent dry rubber 0.307 per cent 

Sliced slab heated to 100 deg. 

C. till dry 0.240 per cent 

Dry crepe from slab (dried 

without heating) 0.21S per cent 

Results on the following data cal- 
culated on the basis of the dry rubber 
present : 

Wet slab 2 hr. after pressing. . . 0.600 per cent 
Wet slab after drying thirteen 

days 0.324 per cent 

Dry crepe from slab 0.220 per cent 

Wet crepe made immediately 

from wet slab 0.396 per cent 

Above crepe when dry 0.360 per cent 

We may summarize the above data 
in the following conclusions : 

(1) Among smoked rubbers from 
the same latex the nitrogen content 
is constant, although the rate of vul- 
canization varies considerably be- 
tween slab and sheet. Smoking ap- 
pears to fix the nitrogen. 

(2) Among unsmoked rubbers 
from the same latex there is a con- 
siderable variation in the nitrogen 
content of the rubber after creping 
preparatory to the vulcanization 
process. It is small in the case of 
rapidly vulcanizing rubbers and 
larger in the case of the more slowly 
vulcanizing ones. 

(3) The low percentage of nitrogen 
in rubber prepared as unsmoked slab 
is attributed partly to loss in the 
gaseous form during the superficial 
drying of the slab, and partly to the 
washing out of nitrogenous decom- 
position products when the slab is 
creped prior to vidcanization. 

(4) Since rapidly vulcanizing 
smoked slab rubber contains as high 
percentage of nitrogen as slowly vul- 
canizing sheets, the actual loss of 
nitrogen cannot be the cause of rapid- 
ity of vulcanization, although it 
would appear from the results of the 
unsmoked rubbers that rapidity of 



52 



RUBBER MANUFACTURE 



vulcanization and loss of nitrogen are 
in some way associated. 

Eaton and Day {Agricultural Bul- 
letin, Federated Malay States IV, 350, 
1916) have followed the change of 
the nitrogen content through the dif- 
ferent stages of handling the latex. 
The results ate summarized in the 
accompanying chart. (Table II.) 

The same coagulum, converted 
directly to sheet and crepe, on the 
day following coagulation contained 
0.40 per cent nitrogen, or about twice 
as much as the other. 

In 1912 Whitby presented before 
the Congress of Applied Chemistry, 
a paper in which he made the claim 
that the natural coagulation of Hevea 
latex was brought about by a coagu- 
lating enzyme. 

Eaton and Grantham carried out 
a series of experiments along this 
line and came to the following con- 



• latex under anaerobic conditions is 
not constant, on some daj r s complete 
coagulation occurring and on others 
much less complete. This is possibly 
due to a variation in the constituents 
of the latex. 

(4) That by the addition of various 
sugars, coagulation under both con- 
ditions always occurs and is due in 
their opinion to the fact that at 
medium is formed more favorable for 
the organisms, which produce coagu- 
lation, and less favorable to those 
producing putrefactive changes. 

In a previous article by these men 
they called attention to the fact that 
an excess of acetic acid in coagula- 
tion retards the rate of cure and upon, 
biological grounds it is explained that 
the micro-organisms which produce 
accelerating substances are killed. To- 
investigate this point, some rubber- 
was coagulated with acid and then 



TABLE II 
Latex. (N T - content 0.11%) 



Wet coagulum remaining 50 
parts Ns 0.20% which is 
equivalent to 0.78% N; on 
dry rubber present. 

Hand rolled after standing 
six weeks to 19.1 parts con- 
taim'ng 0.20% N = or an 
equivalent of 0.23% N« on 
the dry rubber present. 

Washed, creped and dried 
gave 16.4 parts of drv rubber 
containing 0.19% N;; the 
loss here was probably me- 
chanical due to the removal 
of the surface scale which 
had formed and which was 
high in proteins. 



Serum 33 parts (S. G. 1.009) 

No 0.06% 

I 

Held for 14 days with no 

evaporation N2 0.04% 

Held for 60 days with no 
evaporation N2 0.03% 

N!o further loss in NTj. 



elusions {Agricultural Bulletin, Fed- 
erated Malay States, Nov., 1915) : 

(1) That this natural coagulation 
of the latex of Hevea braziliensis is 
due to certain bacteria which infect 
the latex after coagulation. 

(2) That these are two distinct 
types of organisms, one favored by 
aerobic conditions, which tend to in- 
hibit coagulation, and the other 
favored Jay anaerobic conditions, 
which affect coagulation of the latex. 

(3) That the coagulation of the 



soaked in alkaline solutions, thus pro- 
ducing a more favorable medium for 
biological changes to occur. Slab 
rubber was the form chosen with 
which to carry out the test. The re- 
sults were that the rubber cured in 
about one half the normal time. 
Whether this is to be explained upon 
purely a chemical or biological basis 
remains for further research, which 
has been attempted at a more recent 
date. 

If the preceding assumptions are 



DIFFERENT MEANS OF COAGULATION 



53 



•correct that there exists in the rubber 
some substance which has the power 
of decomposing into accelerating 
-compounds, the question arises, What 
is the period during which the change 
in the raw rubber causing accelera- 
tion of rate of cure takes place? 

To answer this question, the two 
■experimenters, above referred to, 
coagulated some latex, then from the 
coagulum removed a sample creped, 
■dried it in a hot air drier and 
then blocked it on the same day 
as coagulated. The next day a new 
sample was taken from the original 
coagulum and treated in the same 
manner: the following day another 
sample, and so on until they had ten 
samples taken in as many days. These 
•were then milled up and cured, 



ber after the tenth day and it will 
remain constant after that time. 
Even samples that have been aged 
seem to retain their accelerating 
bodies. 

In the above, attention was called 
to the remarkable accelerating action 
which alkalis have upon rate of cure 
and it was suggested that this might 
be due either to a biological effect 
or to a purely chemical one. Eaton 
investigated this point in the follow- 
ing manner : 

Samples of both fast curing and 
slow curing rubbers were taken and 
soaked in dilute alkaline and acid 
solutions for twenty-four hours, then 
milled, cured and tested, comparison 
being made in each ease against a 
control sample. 





TABLE HI 






Latex 
Water 
Protein 
Carbohydrates 






Resins 

Mineral Matter 
Rubber 




Mot coagulated. Evap- 




1 

i 


Aerobic Fermentation. 


orated rapidly over CaCl> 
to avoid decomposition 
iand retain all the serum. 

Gave very fast cure rub- 
ber. 


Coagulated by 
Acetic acid 

1 

1 


1 
Anaerobic Fermentation. 

Non-putrefactive. 
Amido compounds 
formed which acceler- 
ated cure. The rubber 
sometimes coagulates 
spontaneously and is al- 
ways coaguable by the 
usual methods. 


■ i 

Proteins putrefy 

Rubber liquefies. 

N'oncoaguable. 

I fastens cure if used 

with coaguable rubber. 


t 




1 
Serum 
1 
Evaporated bv he 

1 




Itubber 

1 
Left with some | 
moisture in 


E. & G. method 
of allowing moist 
slabs to stand G 
davs. Anaerobic. 
Fast cure. 


it 


shipping. Aero- 
bic. Fast cure. | 

Byrne process Slab 

rolled up and 
smoked while 

drying. Anaerobic 

Fast cure 


[ 1 

Protein precipitated 
by heat 


Proteins decom- 
posed anaerobic- 
ally has marked 
accelerating 


Undecoiupused 
portion lias no 
accelerating 



action on slow 
cure rubber. 
Residue after removing insoluble protein evaporated 
to sticky deliquescent mass and desiccated in vacuo. 
Has decided accelerating action on slow cure rubber 
and is stable to putrefactive organisms. Not deter- 
mined whether nitrogenous or not. 



tested, and the following conclusions 
were drawn : 

(1) That the rate of cure increases 
until the sixth day and then remains 
practically constant. 

(2) That the greatest change occurs 
in the first three days. It is per- 
fectly safe, however, to crepe the rub- 



It was found that the alkalis had 
a marked accelerating action upon 
the rate of cure, which was apparent 
in both the fast and slow curing rub- 
bers, while acid had a pronounced 
retarding effect. These tests were 
carried out with finished dried crepes 
so that the biological effect was elim- 



RUBBER MANUFACTURE 



mated and thus the chemical action 
made more certain. However, the 
way in which this chemical effect 
takes place is not known. The evi- 
dence seems to point to the action of 
the alkali upon certain constituents 
in the rubber. The retarding effect 
of mineral acids is especially noted 
with quantities beyond the minimum 
required for coagulation; therefore, 
the serious question of trying to sub- 



stitute sulphuric acid in the place of 
acetic as now used. 

Attention has also been called to 
the fact that rubbers which have been 
treated with alkalis do not show good 
tests upon ageing. 

Let us hope that more work along 
this line will follow and that better 
methods of coagulation will be found, 
thus producing more uniform rub- 
ber from the manufacturer's view- 
point. 



CHAPTER IX 
Theory of the Constitution of Rubber 



To determine the true constitution 
of caoutchouc is no easy matter, as 
will be seen from what follows. In 
the first place, we must be certain 
that we have obtained a pure sample 
with which to work. The fact that 
it belongs in that class of compounds 
which occur in the realm of colloidal 
chemistry does not simplify our task 
to any great extent. 

It has no definite melting point, no 
solution from which it may be crys- 
tallized. Ozone does form with 
caoutchouc an ozonide which is cap- 
able of being purified and studied. 
It was by means of this that Harries 
came to the conclusion that there 
existed a slight chemical difference 
in the constitution of Congo caout- 
chouc and Para. (Annalen, 1913, 395, 
211.) For some time caoutchouc has 
been given the formula of C 5 H s and 
then on account of its analogy to the 
terpenes it is written C 10 H 10 or some 
multiple of this. Faraday and Ber- 
zelius were in possession of this 
knowledge.. 

The first important work along 
this line was done by Gladstone and 
Hibbert. (Trans. Chem. Soc, 188S, 
53, 679.) They tried to obtain pure 
rubber by dissolving it in chloroform 
and then precipitating it with alco- 
hol. Even this method seems to give 
a sample which contains some oxygen. 

They found upon analysis of a sam- 
ple prepared as stated above that it 
contained C = 87.46 and H = 12.00. 
Thev calculated upon the basis of C = 
88.24 and H= 11.7 the formula C-H s . 

We are fortunate, however, in hav- 
ing more evidence as to its formula 
than that of analysis alone. The 
usual methods of determining molecu- 
lar weights, of course, cannot be ap- 
plied here, colloidal solutions showing 



very little if any osmotic pressure 
and not obeying the freezing point 
and boiling point laws of Eoult. 

Bary and Weidert (Compt. Bend, 
1912, 154, 1159) assumed that the 
molecule of caoutchouc was made up 
of several nuclei of five or ten carbon 
atoms each. Then they tried to ex- 
plain that the vulcanization consisted 
in the union of an atom of sulphur to 
each end of a chain of C, H, n com- 
plexes. 

If this is true, then the (C 10 H lc ) n 
has a value of nearly 2500, which 
makes the molecule appear to be a 
very large one. It is also apparent 
that if we continue to vulcanize and 
go on toward ebonite, before that is 
possible, there must be a breaking 
down of this large molecule that more 
sulphur may add itself; or, in other 
words, depolymerization must take 
place. 

It does not seem necessary to hold 
that the caoutchouc molecule is a 
large one. We have two derivatives 
whose molecular weights have been 
determined, the ozonide and nitro- 
sites, and these point to a carbon 
content of ten and twenty atoms. 

Some day we hope to find a solvent 
which will resolve the colloidal ag- 
gregation of a rubber solution into 
a true solution and thus make the 
direct determination of its molecular 
weight possible. 

We know that by certain manipu- 
lations we are able to change the 
aggregations in colloids and thus pro- 
duce substances of different, proper- 
ties. This Harries did in the case of 
caoutchouc {Annalen, 1911, 383. 157) 
and he obtained three materials which 
he designated as a, b and c. 

The a material is obtained by pre- 
- cipitation with alcohol. The b is in- 



55 



56 



RUBBER MANUFACTURE 



soluble and is formed when a is al- 
lowed to stand. The c is an oil ob- 
tained from a by maintaining a tem- 
perature a little above normal. It 
has been suggested that the caout- 
chouc exists in the latex in the c 
modification which is soluble in 
ether. Harries extracted some from 
the latex with ether and. upon stand- 
ing, this changed over into rubber. 
Weber had observed this and put 
forth the idea that this substance 
was a dipentene C 0ft H 30 in the latex 
surrounded by a protein which acted 
as a protective colloid. Therefore, 
when the coagulation reagent is add- 
ed, this protein is removed and at the 
same time the dipentene is poly- 
merized for it becomes insoluble. 
Ilenrichsen and Kindscher (Ber. 
1909, 42, 4329) determined the 
molecular weight of the hydrocarbon 
from the latex by extracting it with 
benzine and determining the lowering 
of its freezing point. This gave a 
molecular weight of over 3000, and 
they felt certain that the rubber 
existed in a colloidal state and that 
it was not a dipentene. In I860, 
Greville Williams . distilled some 
rubber at as -low a temperature as 
possible and, upon refraetioning. ob- 
tained two samples with boiling 
points between 37-40 degs. and 170- 
180 degs., respectively. The first 
portion was mostly isoprene and the 
latter was caoutchine, possessing 
twice the vapor density of isoprene. 
Bouehardat (Compt. rend.. 1879. 89. 
361 and 1117) found that isoprene 
eh a used, when allowed to remain in a 
sealed tube, to a substance having 
a different odor. Then Wallach 
(Annalen, 1884, 255, 311; 1885, 227. 
292: 1887, 238, 88) pointed out that 
this substance was identical with 
caoutchine and dipentene. Then Til- 
den found that dipentene decomposes 
into isoprene and this has been found 
by Wallach to change into caoutchouc. 

Thus we may get the relations of 
these substances as follows: Caout- 
chouc by heat changes into isoprene 
and dipentene; dipentene in a red 
hot tube changes to isoprene ; isoprene 
spontaneously changes into caout- 
chouc ; in a sealed . tube, however, 
isoprene goes into dipentene. Other 



fractions have been obtained and 
studied, but few conclusions have 
been drawn from that source. 

We know that caoutchouc is an 
unsaturated hydrocarbon, but the ex- 
act degree of this unsaturation has 
been a subject of dispute. For 
instance, Gladstone and Hibbard 
{Trans. Chem. Soc, 1885. 53, 679) 
described a chloride of the formula 
C 10 H 14 C1 S , which is best explained 
by assuming the addition of six atoms 
of chlorine thus indicating these 
ethylene groups. 

Harries then tried the action of 
ozone upon a chloroform solution of 
purified Para rubber and obtained a 
compound giving a molecular weight 
according to the formula C 10 H 1G O" . 
By a previous experiment, it was 
found that in ozonides we have three 
atoms of oxygen associated with each 
ethylene group, therefore we must 
have here two such linkages for 
each ten carbon atoms. Harries also 
produced a diozonide of the formula 
C 10 H li; Cv When this was hydrolyzed 
o there resulted hydrogen peroxide, a 
keto- or di-aldehyde, lrevulinic acid, 
and also another acid. To explain 
this, he assumed that the caoutchouc 
molecule may be represented by an 
open chain formula. He later found 
that this was not true, but that the 
primary products of hydrolysis were 
lasvulinie aldehyde and the peroxide 
of lsevulinic aldehvde: 



= 



O: 



= C (CH.,) CH., CH, CH 



= 



-o 



Further hydrolysis of this decom- 
poses it into lrevulinie acid and hydro- 
gen peroxide. 

To account for these two primary 
products of hydrolysis from the 
diozonide and the presence of two 
double bonds to each ten carbon atoms 
requires that the molecule be re- 
garded as a cyclic one, because if it 
were an open chain it would give two 
hydrolysis products oxygenated at 
only one end of their chains. 

Thus Harries suggested that the 
constitution of caoutchouc was repre- 



THEORY OF THE CONSTITUTION OF RUBBER 



sented by the formula of a 1 :5 
dimethylclyclooctadiene : 

CH Q • C • CH„ CH„ • CH 



CH CH 2 • CH 2 • C • CH 3 

Its ozonide is then : 
CH, C • CH CH„ • CH 



CH 



CH„ 



CH., 




Its aldehyde:* 
CH Q C • CH CH 



Its aldehyde peroxide : 
O — 



a 



HC— CH, . CH ; C -CH 3 



Here Harries suggested that poly- 
merization took place due to unsatis- 
fied partial valences which, accord- 
ing to Thiele's theory, is possible 
where we have double bonds in oeta- 
diene ring formation, and thus an in- 
definite number might be linked to- 
gether. 

Pickles (Trans. Chem. Soc. 1910, 
97, 1085) criticises this theory by call- 
ing attention to the fact that if this 
were true, the new polymeride should 
possess a less degree of unsaturation 
than the simple substance, and this is 
not the case. The tetrabromide is 
also formed without any depolymeri- 
zation and yet we have four bromine 
atoms to each ten carbon atoms. 

He also points out that under de- 
structive distillation, we should ex- 
pect to get dimethylclyclooctadiene 
and this is not the case; and yet 
even under reduced pressure we never 
get a substance containing less than 
twenty carbon atoms. Pickles chose 
to assign a chain formula made up 
of C 5 H S nuclei : 



CH, 



CH 



CH. 



"CH„ 



CH(CHA 



CH(CH Q )., 



CH • CH, 



Prom the study of its oxidation 
products, we see that the ends of this 
chain must be linked together. How- 
ever,- the greater amount of favor 
rests on the side of the eight mem- 
bered ring. Willstatter (Ber., 1905, 
38, 1975) was able to prepare clyclo- 
octadiene and this he was able to 
polymerize to form diclyclooetadiene -. 

CH, 



CH. 



CH- 



CH- 



-CH„ 



CH - 



-CH 



-CH.' 



CH 



If isoprene may be made to con- 
dense and form dimethylclyclooc- 
tadiene : 

CH., 



C=CH '■ CH, CH 

I +■ I 

CH : CH„ CH.,= C 



-CH., 



CH — CH., 



CH— CH 



CH- 



CH, 



CH„ 



RUBBER MANUFACTURE 



Showing it in ring form : 
H„ 



CH, — C 




C — CH„ 



then it follows that butadiene should 
yield clyelooetadiene : 

CH=^CH CH.,= CH 



+ 



When Harries compared the ozon- 
ides of butadiene, caoutchouc and 
clyelooetadiene when hydrolyzed, he 
found them to yield the same prod- 
ucts. This furnishes us the evidence 
that caoutchouc is an eight membered 
ring, and from what has been said 
above it does not seem necessary to 
assume that the molecule is any 
larger than C 10 H 16 . 

When the ozonides of purified Para 
and of artificial isoprene caoutchoucs 
are hydrolyzed, they yield the same 
products and thus the conclusion that 
the wild caoutchouc must have the 
constitution of the polymerized iso- 
prene. 



CH- 



->CH. 



CH : CH CH„ : CH 



V 



CH 



CH- 



CH„ 



-CH 



\ 



CH 



CH„ 



CHAPTER X 
Synthetic Caoutchouc 



The question of being able to pro- 
duce artificial rubber is one that has 
interested a great many workmen 
and especially has it been of great 
interest to the laymen of the rubber 
industry. I once heard the superin- 
tendent of a large rubber factory say, 
when asked his opinion as to the pos- 
sibility of synthetic rubber, that he 
expected to see " synthetic apples " 
first. 

Several years ago, certain men and 
in fact we might say certain nations 
began to appreciate the fact that the 
time was approaching when the 
amount of wild rubber then being 
produced would not be sufficient to 
supply the world's demands. To 
meet this condition, Mons. E. Coustet 
proposed three solutions: 

First, he said we must use the 
mineral caoutchouc which had been 
discovered in the Castleton mines, 
England, in 1785, and later in 
France in 1816, and still later in the 
United States. 

Second, we must employ an arti- 
ficial product possessing the prop- 
erties of the natural product. In 
1846, Sacc and Jonas produced such 
a substance by treating linseed oil 
with azotic acid. Another similar 
substance had been produced by 
treating oil of turpentine with sul- 
phuric acid. 

The third suggestion was to in- 
crease the supply of natural product, 
but this seemed like a very slow 
method. 

The first of these suggestions has 
been utilized and in addition to these 
mineral rubbers we are using today 
large quantities of synthetic mineral 
rubber. 

The third way of course has 
proved the method which lias largely 



solved our problem to date, for the 
quantity of the natural product has 
been increased both by obtaining more 
of the wild rubber and by the great 
development of plantations. 

The second idea, that of artificial 
rubber, however, still remains the 
dream of the chemist. It is not a 
question of merely producing it, for 
that has been accomplished, but of 
producing it upon a commercial 
basis. 

How great the demand has been 
for the artificial product is reflected 
in the following statement found in 
the Independent (Sept. 13, 1906, 
61:648-9): "If any ambitious 
young man would like to earn $10,- 
000,000 next year he has the chance. 
The world will gladly pay him that, 
or even more if he will show how to 
make India rubber cheaply. He 
will find much of the preliminary 
work already done; only one link is 
lacking in the chemical process. All 
he has to do is to reverse a well 
known chemical reaction. Any 
freshman chemist can do it — on 
paper. This is all there is to it : 



2C.H. 



-> C 10 H„ 



We know that isoprene results 
from the distillation of caoutchouc. 
In I860, Greville Williams isolated 
isoprene with the apparent formula 
of C 5 H S (Proc. Roy. Soc. 1860, 10, 
516) ; therefore, the above is possible 
and has been accomplished, but not 
on a commercial basis. Bouchardat 
in 1875 (Compt. rend. 1875, 80, 
1446) had observed that some of the 
distillation products of caoutchouc 
could be changed into rubber when 
treated with hydrochloric acid in the 
cold. This substance was undoubt- 
edly isoprene. He also called atten- 



59 



RUBBER MANUFACTURE 



tion to a polymer of this having the 
formula C 10 H 10 . 

Isoprene may be made from tur- 
pentine. In 1882, Sir William Til- 
den (Trans. Chem. Soc. 1884, 45, 
411) observed that isoprene could 
be made from terpenes (substances 
obtained from oil of turpentine). 
He also observed that this isoprene 
upon long standing polymerized into 
rubber. Attempts were then made 
to hasten this reaction. Tilden made 
his isoprene by passing oil of turpen- 
tine through pipes heated to a red 
glow. If the isoprene may be 
cheaply converted into caoutchouc, 
then the raw rubber industry may be 
transferred from the rubber tree of 
the tropics to the pine trees of our 
own country. 

A British patent of 1907, proposed 
by Heinemann, describes the process 
of making synthetic rubber by heat- 
ing a mixture of acetylene and ethy- 
lene at .a dull red heat and there 
results divinyl, 

CH 2 = CH • CH = CH„ 

then by the ordinary reaction using 
methylchloride, this is converted into 
methyl divinyl, or isoprene, 

CH 2 = C • CIT 3 • CH = CH, 

Again the isoprene is made to poly- 
merize into caoutchouc. 

There was a time when the " syn- 
thetic rubber scare " nearly pro- 
duced a panic in the rubber planta- 
tion securities. This furnishes evi- 
dence of the almost unreasonable 
fluctuation of a stock market. 

Harries in 1905 had established, 
he thought, the chemical constitution 
of caoutchouc to be 1.5 dimethyl- 
cyclooctadiene and this aided the 
problem of building up the synthetic 
product {Ber. 1904, vol. 37, p. 2708 ; 
1905, vol. 38, p. 1195). 

In 1910, Harries reported in a 
lecture given in Vienna that he had 
succeeded in converting isoprene 
into caoutchouc by heating it in 
sealed tubes in the presence of 
glacial actetic acid, and he deserves 
the credit of being the first man to 
publish a method for this which 
could be^ repeated by another investi- 
gator. Harries, in 1911, found that 



isoprene in the presence of metallic 
sodium polymerized very rapidly, 
but that the product was different 
from the one obtained' where heat was 
used. (Annalen, 1911, vol. 383, p. 
188). 

In 1884, Tilden also suggested 
that it was possible to potymerize 
the homologues of isoprene and in so 
doing to obtain substances varying 
from resinous bodies up to those pos- 
sessing the properties of rubber. 
This of course suggested new mate- 
rials as starting products in the pro- 
curing of synthetic caoutchouc. 

O. Wallach (Annalen, 1884, 225, 
311; 1885, 227, 292; 1887, 238, 88) 
studied the behavior of isoprene and 
did succeed in polymerizing it by 
means of the action of light. 

Weber repeated the work of Tilden 
and reports that he obtained 211 
grams of caoutchouc from 300 grams 
of isoprene, after keeping it for nine 
months. 

In all this work, it will be observed 
that the isoprene has been obtained 
from some other natural source, but 
in 1897 Euler was able to synthesize 
this substance, (Ber. 1897, 30, 1989 ; 
J. Prakt. Chem. 1898, 57, 131). He 
began with /?-methyl pyrrolidine 



C H3 — CH — C Ho 



CHo-CH 



NH 



and by successive treatment with 
CH3I and KOH was able to produce 
isoprene : 

CH 3 -C=CH, 

I 
CH = CH a 

It is apparent, therefore, that the 
product which results depends upon 
the method used and also upon the 
material used in starting, as is shown 
by the statements of Holt in Z. angew. 
Chem. 1914, vol. 27, p. 153. 
Caoutchoucs from Butadiene, C 4 H 6 

Normal caoutchouc : (by heat- 
ing), easily soluble, elastic, vulcan- 
izable. 

Carbon dioxide caoutchouc : In- 
soluble, does not swell up, moderately 
elastic, unvulcanizable. 



SYNTHETIC CAOUTCHOUC 



Sodium caoutchouc : Easily solu- 
ble, elastic, vulcanizable. 
Caoutchoucs from Isoprene, C 5 H S 

Normal caoutchouc : Easily solu- 
ble, elastic, vulcanizable. 

Carbon dioxide caoutchouc : In- 
soluble, does not swell up, elastic, 
vulcanizable. 

Sodium caoutchouc : Easily solu- 
ble, not elastic, difficultly and incom- 
pletely vulcanizable. 

Caoutchoucs from Dimcthylbuta- 
diene, C H 10 

Normal caoutchouc : Easily solu- 
ble, not elastic, can only be vulcan- 
ized to hard rubber. 

Carbon dioxide caoutchouc : In- 
soluble, does not swell up, not elastic, 
difficultly vulcanizable, easily oxidiz- 
able. 

Sodium caoutchouc : Soluble and 
insoluble modifications, not elastic, 
un vulcanizable. 

From the above table, it may be 
seen that by properly choosing the 
material to start with, and by use of 
the proper process of polymerization, 
it is possible to obtain caoutchouc 
with entirely different properties. 

CH 3 



This has a suggestion in it of tech- 
nical importance for it points out the 
fact that some day we may be able to 
produce and emphasize any particu- 
lar property that is desired. 

The first thing to be accomplished 
is the production of isoprene or its 
homologues, then a method of polym- 
erizing these substances. Both of 
these processes must be such as can 
be worked on a commercial basis and 
must produce a final product with 
chemical and physical properties 
analogous to the native rubber and at 
a cost to compete with the native 
rubber. 

We shall now consider different 
means of producing isoprene. It was 
noted above that Tilden obtained 
about a five per cent yield of isoprene 
from turpentine, but even though a 
good yield could be obtained, the 
supply of turpentine is very variable 
and uncertain. Several men have 
carried out valuable investigations 
along this line. Neresheimer (Inaug. 
Dissert. Kiel, 1911) began with the 
diethyl ester of pyrotartaric acid, 
which he reduced by means of 
sodium and then the following steps 
as indicated here : 



CH 3 



CH, 



I | 

CH • COOC 2 H 5 Reduction CH • CH 2 OH 

with ^ I 

Sodium 
CH 2 -COOC 2 H 5 CH a CH s OH 



I I 

CH • CH 2 OH w . th CH • CH a Br 

HBrH 
CH 2 CH s OH CH 2 -CH 2 Br 



CH, 



CH 3 



N(CH S ) 3 



with ^ CH • CH 2 N(CH 3 ) 3 Br 
CH 2 CH 2 N(CH 3 ) 3 Br 
CH, 



ith CH • CH 2 N(CH 3 ) S OH 



Ag 2 



CH 2 CH 2 N(CH 3 ) 3 OH 



Distillation 



>C= CH 3 



C -H : CH 2 

This method has the great advan- 
tage of producing a pure product. 
Matthews and Strange (English Pat. 
4189, 1910) worked out a different 
method starting with isopentane, 



CH, 
CH- 



: ^>CH-CH 2 -CH 3 



first converting it into the dihalogen 
compound, 

CH 3 \ 
CH 8 Br> CH - CH *- CH * Br 

From this the halogen acid is then 
removed and isoprene results : 

CH 3 \ 
CH 2 > C ' CH:CH2 

Then later we find another process 
beginning with the same substance 
when the Badischer Anilin und Soda 



RUBBER MANUFACTURE 



Fabrik (Fren. Pat. 43512, 1911) ob- 
tained isoprene by tbe following 
steps : 

CH >CH-CH. 2 -CH 3 



CH 8 

CH S 



is converted into the nionohalogen, 

a ^CH-CHBr-CH 3 
this when treated with lime yields 
3> ">C=CH-CH 3 



CH S 
CH 8 



triniethylethyleiie. This is then eon- 
verted into the dihalogen derivative, 



CH 3 
CH S 



•CBr-CHBr CH„ 



and when this is passed over a cata- 
lytic agent under reduced pressure 
at a temperature of 350 deg., isoprene 
results. 



CH; 

CH ; 



C-CH=CH„ 



The Bayer Co. next produced iso- 
prene, beginning with a coal tar 
product. They used p-cresol which 
is first reduced and then oxidized 
and this treatment will break the 
ring structure. The steps are indi- 
cated as follows : 

CH, 

C 



CH 
CH 



CH Reduction 



CH 



Oxidization 



C 

I 
OH 

CH S 

CH-CHoCOOH 
""CH.;CHoCOOH 



CH 3 

CH • CH 3 CONH, HCIO. 
CH 2 CH 2 CONH 2 



CH 3 
>CH-CH 2 NH 2 

CH, CH., NH, 



CH, 



Methylation 



> C : CH 3 is isoprene. 



CH:CH 2 

Heinemann {Ejig. Pat.13252, 1908) 
proposed that by the hydrolysis of 
starch, then oxidization and treat- 
ment with phosphorus trisulphide, 
there would result methylthiophene 
which upon reduction would give 
isoprene. This is the method which 
gained wide newspaper publicity for 
it suggests the production of auto 
tires out of potatoes. 

Harries (Annalen, 1911, 383, 157; 
worked out a method starting with 
alcohol, the necessary steps of which 
method are indicated here : 



CH 3 CH 2 OH— >CH 3 COOH- 

>(CH 3 ) 2 • C(C 2 H 5 )OH— ; 

>CH 3 CHBr CBr (CH 3 ) 2 - 



^■CH 3 COCH 3 
CH 3 -CH:C:(CH 3 ) 3 
^CH 2 :CH-C^CH 3 



This method becomes a possibility 
inasmuch as commercial alcohol is 
now available. It is claimed for this 
process that it will yield from 60 to 
75 per cent pure isoprene. 

Matthews and Strange {Eng. Pat. 
4572, 1910) then carried out some 
work with the amyl alcohols, both the 
iso and active, found in fusel oil. 
By carefully chlorinating these sub- 
stances, passing the products over 
soda lime heated to 470 cleg, and then 
fractionating, they claimed to have 
obtained a forty per cent yield "of 
isoprene. 

This constitutes a brief survey of 
the attempts which have been made 
to produce isoprene, the substance 
which by polymerization we are able 
to convert into caoutchouc. 

Next in order, therefore, we must 
consider the ways which we have for 
effecting this latter change. 

Some of these have already been 
mentioned, for example, its treat- 



SYNTHETIC CAOUTCHOUC 



nient with acid, autopolymerization, 
light, etc., all of these processes being 
slow and producing uncertain re- 
sults. It was to hasten this process 
that heating in sealed tubes and then 
treatment with acetic acid was tried. 
From the use of these substances to 
accelerate the change, we find almost 
every class of compounds, both or- 
ganic and inorganic, being used, even 
down to the Koentgen rays. 

The caoutchoucs prepared by the 
above reagents will respond to tests, 
which Harries laid down for a true 
caoutchouc and thus these are called 
" normal caoutchoucs." 

Then Harries and Matthews inde- 
pendently found that sodium or even 
amalgams, either hot or cold, would 
polymerize isoprene either in the cold 
or with a little heat, and effect this 
change almost, quantitatively. This 
final product does not yield the same 
ozonide as the normal caoutchouc, in- 
dicating that it must possess a differ- 
ent constitution. As stated in the 
beginning, Tilden suggested that it 
was possible to produce caoutchouc 
from the homologues of isoprene ; 
also, therefore, we shall discuss 
briefly the one most commonly used 
and the one which has given the best 
results, namely. Butadiene. Harries 
started with ethylmethylketone and 
reduced it to sec-butyl alcohol, which 
may be dehydrated, then by produc- 
ing the dibromide and treating this 
with soda lime, butadiene results. 

Hexahydrophenol has been con- 
verted into butadiene by heating it 
to a temperature of 600 deg. C. 

It was observed by Ehrlich in 
1905 that the addition of amino 
acids would increase the pro- 
duction of higher alcohols in 



-CH 3 =CH-CH=CH a 



fusel oil during fermentation. With 
this idea,, Fernbach and Strange 
worked out a cheap method of pro- 
ducing butyl alcohol and acetone. 
This alcohol is then converted into the 
chloride, and then by chlorination into 
the dicnloride, which when heated 
with soda lime will produce butadiene, 

CH 3 CH 2 CH 2 CH 2 OH 

CH S CH 2 CH 2 CH 2 CI 

CH 3 CH 2 CHC1 CH 2 CI or 

CH S CHC1 CH 8 CH 2 ClorJ 

CH 3 C1 CH 2 CH 2 CH 2 C1 

The Synthetic Products Co. suc- 
ceeded in converting butyl aldehyde 
into the aldol, and this when reduced 
gives the 1,3-butyleneglycol ; this is 
converted into the dichloride, and 
when treated with soda lime butadi- 
ene results. 

CH S CHOH CH 2 CH0^CH 3 CHOHCH 2 CH a OH- 
CH 3 CHC1 CH 2 CH 2 C1— >CH 2 =CH • CH=CH 2 

Butadiene 
Several other methods have been 
used to produce this substance, and 
in fact several other homologues have 
been produced. The methods used 
to polymerize butadiene are similar 
to the ones used upon isoprene. The 
sodium butadiene seems to be the 
best, however. The polymerization 
is complete in about three hours if 
it is held at a temperatiire of from 
forty to fifty degrees. 

This constitutes a brief survey of 
the synthetic rubber industry up to 
date. Although it is very promising 
from the standpoint of the work 
which has been done, yet a great deal 
more remains to be done before the 
natural rubber securities need be dis- 
turbed again either in the United 
States or in Europe. 



CHAPTER XI 
Chemical and Phvsical Testina of Crude Rubber 



As in the analysis of every sub- 
stance, so in the analysis of crude 
rubber, the chemist must first obtain 
what may be regarded as a uniform 
sample. This, at first thought, seems 
a very simple matter, and yet it is 
one that causes as much if not more 
trouble than any other step in the 
complete analysis of any substance. 

It is obvious that the analysis of a 
few ounces of rubber is absolutely 
worthless unless the sample is truly 
representative of the entire lot whose 
composition is desired. Therefore, a 
few general directions are necessary 
for the obtaining of what may be 
regarded as uniform a test lot as pos- 
sible. 

Rubber comes into the market in 
extremely varying forms and lots. 
Of course, the more uniform the 
rubber the easier it is to obtain a 
good sample and vice versa. The 
plantation rubber is comparative- 
ly easy to sample. It will be re- 
membered that the rubber comes 
into the market in the form of sheets. 
blocks or slabs, balls, spindles, 
thimbles, twists, sausages, scraps of 
every size and shape, biscuits, etc. 
Some shipments are small, others are 
large : some of the above forms are 
small and some large. It naturally 
follows, of course, that the smaller 
the forms and the smaller the ship- 
ments, the easier the task of sampling. 

As an example, let us select a sam- 
ple from a large shipment, made up 
of many containers of which the fomis 
are rather large. Enough of the 
containers should be opened and thor- 
oughly inspected to learn whether it 
may be regarded as a uniform ship- 
ment, thajt is. whether each package 
is a representative sample of the 



whole. If this is true, then a sample 
need not be taken from each package, 
but only from every other one or 
every third one. This, of course, is 
to be judged from the general appear- 
ance of the lot. If the forms are also 
running large, samples may be cut 
from representative ones taken. This 
will keep the volume of the sample 
down and at the same time not impair 
its uniformity. When cutting a ball 
or slab, it must be cut completely 
through. Some take a slice diagonally 
through the form while others take 
one through the middle perpendicular 
to the long axis. Ordinarily, sam- 
pling is not pleasant work and is, 
therefore, sadly neglected. A sample 
is wanted, some inexperienced help is 
often sent to get it and he does so with 
the least possible expenditure of en- 
ergy and thought. Too much emphasis 
cannot be placed upon this first and 
very important step in the analysis 
of rubber, or, in fact, any substance. 

W ashing Loss 

The sample having been obtained, 
the first thing to be done is to deter- 
mine what is called the " washing 
loss." This will include in its per 
cent that due to moisture, dirt, and 
the soluble non-rubbers, which in- 
clude proteins and carbohydrates. To 
determine the washing loss, the larger 
the sample taken the better : there- 
fore, this test is better carried out on 
a factory scale than in the laboratory. 
A batch of rubber is first of all sub- 
jected to the washing process, just 
what method to be used depending 
upon the grade of crude rubber. If 
it comes in large, somewhat hard 
forms, it may be softened first in 
warm water and then cut up into 
suitable sizes to pass through the 



64 



CHEMICAL AND PHYSICAL TESTING OF CRUDE RUBBER 



washer. The rolls are set rather far 
apart at first and water plays over 
them. As the rubber passes between 
the rolls, it soon takes the crepe form 
and the washing continues until the 
impurities are all removed. The rolls 
are gradually brought closer together 
so that a thin crepe may be obtained, 
thus enabling the rubber to dry more 
quickly. The thickness of these sheets 
varies greatly in different factories. 
After this it is dried and the loss in 
weight which it suffers, calculated in 
per cent of the original batch, repre- 
sents the ' ' washing loss. ' ' 

This is a test which has great in- 
fluence in determining the value of 
wild rubbers. On account of the 
cleanly methods of handling, the 
plantation rubbers run the lowest in 
washing loss while some grades of 
African run over fifty per cent wash- 
ing loss. 

A list of the more common rubbers 
with their average results of analysis 
is given on another page. If the de- 
termination has to be carried out on a 
laboratory basis, great care must be 
exercised in selecting the sample, for 
misleading results may be obtained 
unless it is very carefully supervised. 

From the analysis of crude rubber, 
not a great deal is to be gained. We 
shall present the tests ordinarily car- 
ried out in the order of their im- 
portance. 

Determination of Moisture 

First, the moisture present in rub- 
ber must be determined. Moisture may 
cause a great deal of trouble in differ- 
ent manufacturing processes and, 
therefore, before being used, the rub- 
ber must be thoroughly dried. This is 
a test which it is not necessary to carry 
out in the chemical laboratory very 
often, for a man with much ex- 
perience in handling rubber is soon 
able to judge as to the amount of 
moisture present in a sample, or at 
least as to whether or not it is dry 
enough to be used in compounding. 
If it is imperative to carry out this 
test in order to trace some trouble, 
then the best method consists in heat- 
ing five to ten grams of the sample, 
reduced to as small parts as possible, 



in a vacuum oven until it comes down 
to a constant weight. This will re- 
quire only a short time with some rub- 
bers and a comparatively long time 
with others. Sometimes we see this 
test being carried out in an ordinary 
hot-air oven. Comparative results 
may be obtained by this method, but 
it is not to be recommended. The 
best and most accurate method con- 
sists in allowing the rubber to stand 
over sulphuric acid in a vacuum dis- 
sicator at normal temperature. 

The tendency of rubber to oxidize 
with elevation of temperature must be 
guarded against. The unvulcanized 
rubber is less susceptible to this in- 
fluence than the vulvanized. 

Theoretically, we want to dry the 
rubber in the shortest possible time 
at the lowest temperature possible. 
This, of course, is effected by drying 
in a vacuum, the temperature used 
being generally about 60 deg. C. If 
a hot-air oven must be used, 105-110 
deg. C. is used. At this temperature 
and, in fact, at 60 deg. C, some rub- 
bers running high in a flabby resin 
become very soft and tacky and it is 
hard to remove the last traces of mois- 
ture, likewise they are more apt 
to oxidize. To obviate the difficulty 
of oxidization, during the drying, 
Obach devised a method whereby he 
dried the rubber in a stream of dry 
carbon dioxide and then absorbed the 
moisture in a weighed U-tube contain- 
ing sulphuric acid. This method de- 
termines the moisture directly, but is 
more or less difficult to control. 

The percentage of moisture by what- 
ever method determined, is calculated 
from the ratio of the loss during heat- 
ing to the amount taken in the be- 
ginning. As a limit of water present 
in rubber for compounding, we may 
allow as high as 0.5 of a per cent. As 
before stated it is necessary ' only to ' 
perform this test occasionally to check 
up the efficiency of the drying system 
in use. 

Estimation of Resin 

The next determination is the one, 
which is no doubt carried out more 
than any other, namely, the estima- 
tion of the amount of resin. The prin- 
ciple, upon which this determination 



66 



RUBBER MANUFACTURE 



is based, consists in extracting a 
known weight of the washed and 
dried rubber with a solvent which 
will remove the resin. Acetone is the 
one used. The solvent is then evapo- 
rated in a weighed flask and the resin 
thus determined. 

To actually carry out this test you 
should proceed as follows : A weighed 
amount of rubber, which has been 
washed and dried, is placed in an ex- 
tractor, and here we might say that 
the form used depends on the wish 
of the operator. Many different 
forms are on the market. Of course, 
the Soxhlet form is good and has 
been and still is used a great deal. 
The Wiley extractor has been used 
with considerable success. The writer, 
however, at present is using the 
Bailey-Walker form and is well sat- 
isfied with its results. The great ad- 
vantage in it comes in its compact- 
ness and the fact that the solution of 
the resin in acetone does not have to 
be transferred to a tared flask for 
weighing. The acetone used in these 
determinations should be freshly dis- 
tilled off from potassium carbonate. 

The larger the amount of rubber 
taken, the more accurate will be the 
result; therefore, let the size of the 
thimble in the extractor determine 
how much it is possible to take. The 
rubber is reduced to as small pieces as 
possible so that the maximum solvent 
action of the acetone will be had. 
Some rubbers when treated in this 
manner and then subjected to extrac- 
tion, become very soft and tend to 
flow together, thus making complete 
extraction impossible. In cases of 
this kind, the rubber may be sheeted 
out as thin as possible on a mill. Then 
a weighed ribbon of this is rolled up 
in muslin and placed in the extrac- 
tion thimble. The extraction is then 
begun by heating the acetone in the 
flask either over a water bath or elec- 
tric hot plate and continued for a 
period of ten hours. This is ample 
time for the extraction if the sample 
has been properly prepared and the 
necessary precautions taken. The ace- 
tone is then evaporated off over a 
water bafh and the flask is heated 
for three hours in an oven held at 
105 to 100 deg. C 



One must be very careful as 
some resins are volatile at this tem- 
perature and thus a loss might be en- 
countered. In fact, it was recently 
observed in our laboratory that there 
were present in some rubbers resin 
which would volatilize at just a few 
degrees above the boiling point of 
acetone. It is still an undecided ques- 
tion in the mind of the writer as to 
whether or not there are some which 
distill over with the acetone. 

The percentage of resin is calculated 
on the basis of the rubber taken. The 
resin content varies within wide 
limits when we are considering all 
kinds of rubber, but varies within 
narrow limits for the same variety of 
rubber. For instance, Hevea will 
run about 3 — 4 per cent; plantation 
about 2 — 3 per cent, while Accra 
Lump will run from 30 — 40 per cent. 
The resins from South American rub- 
bers are generally liquid and of a 
dark color. Plantation resins are also 
liquid, but of a lighter color. The 
African resins are generally yellow 
and more or less brittle, but soften 
with heat. 

The amount of resin in a rubber is 
not an absolutely reliable criterion 
as to the value of rubber for manu- 
facturing purposes. Ordinarily the 
low resin content rubbers are best for 
the resin may be considered really as 
a diluent. 

Determination of Ash 

The next determination of value is 
that of ash. The principle of this 
determination consists simply in in- 
cinerating a weighed amount of 
washed and dried rubber and thus 
obtaining the amount of mineral mat- 
ter in the sample. 

To carry out this test, as large a 
sample as possible is used and weighed 
into a large shallow formed crucible 
of known weight. Heat is very care- 
fully applied and regulated so that 
the volatile substances will not take 
fire. Should this happen, they may 
be easily extinguished by superim- 
posing the cover over the crucible. 
When the volatile products are re- 
moved, the heat is increased up to 
that of dull redness and held there 



CHEMICAL AND PHYSICAL TESTING OF CRUDE RUBBER 



67 



until all carbonaceous material has 
disappeared. The weight of the re- 
sidue is then obtained and its per- 
centage calculated on the basis of the 
rubber taken. 

The ash content of rubbers does not, 
or rather should not, vary within large 
limits. In fact, in the majority of 
rubbers, regardless of their source, the 
per cent should run from about 0.5 
of one per cent up to 1.5 per cent. 
There are a few exceptions to this, 
however, and we find an ash as high 
as 3 per cent. The determination of 
the ash is of value for two reasons: 
First, it serves as a check upon the 
effectiveness of the washing process, 
for if it has been done hastily and in- 
completely, the ash will of necessity 
run high. Secondly, it serves as a 
means of detecting non-rubber mate- 
rials. These determinations are the 
chemical tests most frequently carried 
out and the ones upon which the ver- 
dict of the investigator is largely 
based. 

Determination of Nitrogen 

Where a complete analysis is re- 
quired, it becomes necessary to de- 
termine the proteids and other nitro- 
genous matter in the rubber. These 
cannot be determined directly, but we 
simply multiply the amount of nitro- 
gen found by analysis by the factor 
6.25. Not knowing the true nature of 
the rubber proteins, it is hardly neces- 
sary to say that this test does not fur- 
nish us with any reliable information. 
The test is carried out as follows: 
About two grams of rubber are 
weighed out and placed in a long- 
necked Kjelclahl flask, when 30 cc. of 
concentrated sulphuric acid and a 
drop of mercury are added. It is well 
to loosely cork the flask by putting a 
small funnel in the neck of the Kjel- 
dahl. Heat is then applied to the flask, 
very carefully at first, until the first 
violent reaction has subsided. Then 
the heat is gradually increased until 
the acid boils quite vigorously. This 
is continued until the contents of the 
flask acquire a straw yellow color. 

The solution is very cautiously 
diluted, and in some cases trans- 
ferred into a larger flask, although the 
using of a large Kjeldahl in the be- 



ginning avoids this step. After dilu- 
tion, one or two grams of sodium sul- 
phide are added, then caustic soda, 
until the solution is distinctly alka- 
line. A few pieces of scrap zinc will 
prevent pounding when it comes to 
distillation. 

The nitrogen of the original rubber 
lias been converted into ammonium 
sulphate by the above treatment. 
Upon the solution having been made 
alkaline and upon the application of 
heat, ammonia will be distilled over 
into a known amount of N/5 sul- 
phuric acid. When the ammonia is 
all driven over, the excess of acid is 
titrated back with N/5 alkali, using 
methyl orange as an indicator. Prom 
the amount of acid consumed during 
the distillation, the amount of nitro- 
gen in the rubber taken is calculated 
and from this the protein. The nitro- 
gen in some unwashed rubbers may 
run as high as one per cent. Of this 
considerable is due to albuminoids 
which are present in the rubber, but 
which are soluble and would be re- 
moved upon washing. It is the al- 
buminoid nitrogen which undergoes 
putrefaction and imparts to the rub- 
ber a bad odor. It also has a dele- 
terious effect on the rubber. This 
albuminoid nitrogen is sometimes 
determined by determining the dif- 
ference between the nitrogen in the 
unwashed and washed rubber. A 
small percent of nitrogen in rubber 
is a sign of strength rather than of 
weakness in the rubber. 

Determination of Insoluble Matter 

The determination of insoluble 
matter is sometimes required. As the 
term implies, it includes those sub- 
stances which are insoluble in the 
ordinary rubber solvents. Under in- 
soluble matter, Ave find sand, clay, 
wood, humus, and other accidental 
impurities. 

Theoretically it is an easy matter 
to treat a known amount of rubber 
with a solvent and weigh the residue, 
thus obtaining the insoluble matter, 
but the extreme viscosity of rub- 
ber solutions makes it a difficult mat- 
ter to separate the insoluble from 
the soluble. 



RUBBER MANUFACTURE 



The methods employed give best 
results if the crude rubber is first 
milled when the pectus modification 
is broken down, and solution results 
more readily. A known amount of 
rubber is treated with either toluene 
or phenetol, the latter having been 
used by C. Beadle and H. P. Stevens. 
Even petroleum may be used and 
gives a solution, which may be fil- 
tered through a tared filter or centi- 
fuged and the residue determined. 

Determination of Rubber 

The insoluble matter as a rule runs 
a little lower than the ash as some 
of the inorganic matter exists as salts 
which are soluble in the solvents 
used. The determination of rubber 
proper, or the pure hydrocarbon, is 
generally obtained by difference, that 
is, the combined percentage of mois- 
ture, ash, organic protein, and ace- 
tone extract subtracted from 100. It 
may be determined directly, how- 
ever. One or two grams of rubber 
are put into solution as indicated 
under insoluble matter and then al- 
lowed to settle of its own accord, or 
is hastened by centrifugal force. It 
is diluted up to 100 cc. and then 
50 cc. are pipetted off and dropped 
into 100 cc. of warm alcohol, when 
the pure hydrocarbon is precipitated. 
To purify it the caoutchouc is pre- 
cipitated several times, then dried in 
a weighed disk in a vacuum and its 
weight determined. 

Instead of precipitating the rub- 
ber from the 50 cc. of solution it 
might have been transferred to a 
weighed flask, and the solvent evapo- 
rated off. The resin can then be re- 
moved by repeated washing with 
boiling alcohol under a reflux con- 
denser. It may then be dried and 
its weight ascertained. The higher 
the resin content, the less accurate 
are both of these methods. 

Its determination by formation of 
the tetrabromide has been outlined 
by Spence and Galletly. They first 
dissolved a small amount of rub- 
ber in carbon tetrachloride. To this 
they added a reagent composed of 
6 cc. of bromine and one gram of 
iodine in .one liter of carbon tetra- 
chloride, and allowed to remain about 



six hours. When this solution is 
added to alcohol, the tetrabromide is 
precipitated. It may be purified by 
dissolving it in carb'on disulphide 
and reprecipitating it with petroleum 
ether. This may be repeated if nec- 
essary. The pure tetrabromide is 
then fused with a mixture of sodium 
carbonate and potassium nitrate. The 
residue is taken up in a small amount 
of water, nitric acid added, boiled 
and the silver halide determined. 
From this the amount of rubber 
proper is calculated. A great deal 
has been published concerning this 
method and it has its merits in prin- 
ciple at least, but in the hands of the 
writer, it has never given concordant 
results. 

Viscosity of Rubber 

Schidrowitz and Goldsbrough 
(J.S.C.I., 1909, p. 3) have called at- 
tention to some very interesting re- 
sults from experiments upon the vis- 
cosity df rubber and its solutions. 
They point out that as is known, the 
viscosity of a liquid or of a solid 
contained in a liquid depends upon 
the state of aggregation of the mole- 
cules or physical' aggregation. There- 
fore, the viscosity of rubber solu- 
tions should throw some light upon 
the chemical or physical state of ag- 
gregation in the rubber solution and 
this should give some idea as to the 
" nerve " of the rubber under con- 
sideration. The results of this work 
lead Schidrowitz to conclude that 
" Within the same species, viscosity 
measurements give a direct line as 
to strength and vulcanizing capac- 
ity. Comparing species with species, 
this does not hold good directly, 
probably because different species 
possess differently constituted mole- 
cules, and the relationship is, there- 
fore, of a more complex order than be- 
tween different specimens of the same 
species. At the same time the broad 
proposition holds good for all species, 
compared inter se or otherwise, that 
high viscosity figures indicate 
strength and low viscosity figures, 
weakness." 

Specific Gravity 

Specific gravity is sometimes de- 



CHEMICAL AND PHYSICAL TESTING OF CRUDE RUBBER 



termined, any one of the general 
methods for such work being em- 
ployed. The information to be gained 
from this determination does not in- 
fluence the judgment of the investi- 
gator to any extent. Only on rare 
occasions is it carried out on crude 
rubber, but it is used a great deal on 
vulcanized goods. 

Sun Cracking 

Another test, which has been sug- 
gested to be used upon' both crude 
and vulcanized rubber, is known as 
the effect of " sun cracking." 

To test the liability of rubber, to 
sun*crack requires a long period of 
time, and that, of course, renders the 
test almost useless because we do not 
have time to waste in waiting for a 
test that consumes a large amount of 
time. However, to obtain a test, 
which will show this property of the 
rubber, several artificial methods 
have been recommended. Weber sub- 
jected weighed samples' of rubber, 
presenting the same area, to the ac- 
tion of acetone peroxide for two days. 
The samples were then removed, 
dried, weighed, and the increase in 
weight was to be considered as a 
measure of the liability of the rubber 
to sun crack. He claims that the re- 
sults obtained were in agreement 
with the actual results obtained by 
carrying out the sun-cracking test. 

Ditmar tried to obtain a set of 
comparative results illustrating the 
same property of rubber. He placed 
in glass tubes weighed samples of 
rubber, then passed oxygen into these 
until the air was all excluded, when 
the tubes were sealed. These were 
then heated in a Carius furnace for 
from five to twenty hours at a tem- 
perature of 100 deg. C. The sam- 
ples of rubber were then removed 
and weighed and their increase in 
weight he hoped to be a measure of 
the liability of the rubber to sun 
crack. He later modified his test by 
placing the rubber in a tube supplied 
with ground valves at each end and 
he maintained a constant tempera- 
ture by lowering this tube into boil- 
ing water. Whether the results ob- 



tained are of much value is a ques- 
tion. 

Vulcanizing Test 

After all of these tests have been 
outlined and after a sample has been 
subjected to all of them, the question 
which would still remain unanswered 
is the one, which is perhaps oftenest 
asked by the manufacturer: How 
will the rubber conduct itself dur- 
ing vulcanization? It is true some 
general idea of this may be inter- 
preted from the results obtained 
above, but the only conclusive infor- 
mation is to be gained by trying it. 

In fact, some laboratories base 
their entire opinion of crude rubber 
upon the information gained by ac- 
tual vulcanizing and physical tests 
which follow. 

A certain test formula is agreed 
upon and all samples of rubber to be 
tested are milled up according to this 
and then subjected to vulcanization 
at a certain temperature. Samples 
are removed at equal intervals and 
thus the rate of cure in the rubber 
may be obtained. Tensile strength 
strips may then be made and the 
physical tests carried out. These are 
the tests which interest the practical 
man. Little does he care whether a 
sample of rubber runs high or low in 
resins if it will cure in a short time 
and produce what he regards as a 
good stock. The technical man, on 
the other hand, is interested in try- 
ing to figure out the relation and in- 
fluence of each of the above tests 
upon the product finally to be ob- 
tained in actual working conditions. 

In addition to all the foregoing in- 
formation, before final judgment is 
pronounced in regard to a given sam- 
ple of rubber, its life history should 
be known : where it came from, liow 
it was obtained, to what species it 
belongs, how it was coagulated, how 
it was stored, its form, color, odor, 
and many more questions of a simi- 
lar nature. 

With all of this, knowledge before 
one, a proper conclusion in regard to 
the merits of a sample of rubber 
should be easily arrived at. 



RUBBER MANUFACTURE 



Below is a table taken from Cas- 
pari, which shows the relations of 
different rubbers in regard to the 
three most important tests : 

Washing 

Rubber. Loss. Resin. Asb. 
Para Hard Fine, 

Para. Bolivian Fine.. 16-21 2.5-3.5 0.2-0.4 

Manaos Scrappy 20-25 1.6-2.0 0.6-0.7 

Para Negrohead, Ser- 

nambv 30-40 3.0-6.0 0.5-1.5 

Camera' 45-50 1.4-1. S 0.5-0.8 

Mattogrosso Virgin 18-22 2.5-3.0 0.5-0.7 

Mattogrosso Negrohead.. 20-25 1.5-2.0 1.5-2.0 

Mollendo Fine 15-20 1.8-2.0 0.2-0.3 

Mollcndo Coarse 12-18 2.0-2.5 0.3-0.4 

Caucho & Peruvian Ball. 20-30 3.0-5.0 0.5-1.5 

Manicoba 25-35 2.8-3.0 3.0-4.5 

Ceara Negrohead 20-30 4.0-5.0 1.0-1.5 

Mangaheira 30-40 20-25 1.0-1.5 

Central American 20-40 4.0-7.0 1.0-2.5 

Guayule 22-26 20-35 1.0-1.5 



Sierra Leone, Conakry, 

Massai, Soudan 15 

Bassam, Cape Coast, Ac- 
cra, Labou. Ivory Coast, 

Gold Coast 25 

Second-Accra Lump, Salt- 
pond I 

Gambia, Bissao i 

Gaboon, Loango, Congo 

Ball .: 

Lagos, Niger, Penin .... 30 

Batanga, Cameroon 25 

Lower Congo. Wamba. . . 
Angola. Loanda, Benguela, 

Upper Congo sorts 5 

Mozambique, Beira 

Madagascar, Tamatave. 

Majunga 2 

Assam 1 

Penang 1 

Borneo 35 

Java Plantation 1 

Ceylon and Malayan Plan 

tation 

Plantation Rambong. . . . 



30 5.0-7.0 0.4-1.0 



.40 7.0-11 0.7-1.0 



)-40 


29-3S 


1.4-2.0 


)-50 


5.0-6.0 


1.0-2.0 


>-35 


8.0-18 


0.6-1.0 


'-40 


10-25 


0.3-0.7 


-35 


10-15 


0.5-1.0 


:'o 


5-6 


0.5-1.0 


5-4(1 


5-7 


1.0-2.0 


-15 


4-10 


0.5-1.5 


-15 


5-8 


0.1-0.8 


1-30 


7-10 


0.2-0.5 


>-35 


5-11 


0.5-1.0 


»-80 


5-7 


0.3-0.7 


1-45 


10-11 


0.4-0.6 


L-2 


5-6 


0.3-0.4 


-?. 


2.5-3.5 


0.2-0.6 


1-2 


7-8 


0.2-0.3 



CHAPTER XII 
The Manufacture and Use of Inorganic Fillers 



It will be our idea in this chap- 
ter to give the reader some infor- 
mation in regard to the manu- 
facture of the materials which are 
used in compounding rubber and 
why certain materials are used. In 
the vast majority of eases, little is 
known of the substances used in com- 
pounding and it seems that the in- 
creasing of this knowledge should add 
interest to the subject and everyone 
will grant that increased interest 
tends toward greater efficiency. 

Far be it from us to deal at any 
length with all the inorganic com- 
pounding ingredients, or even to men- 
tion them. We shall simply pick out 
what may be regarded as the com- 
monest ones, those used in practically 
every factory to a greater or less 
extent. 

In order to present this matter in 
some definite system, the writer will 
group these ingredients under four 
headings : 

First — Substances essential for vul- 
canization. 

Second — Accelerators . 

Third — Fillers. 

Fourth — Pigments, which will be 
subdivided into classes according to 
colors. 

This is not the only classification 
and perhaps it is not the best one but 
it will serve our purpose here. These 
different groups overlap as will be 
seen from the order which follows. 

Under the first group we shall con- 
sider sulphur, which we may say is 
essential in all processes of vulcani- 
zation ; sulphur chloride ; carbon .bi- 
sulphide and carbon tetrachloride, 
which are used in certain kinds of 
vulcanization. 

Under the second class, inorganic 
accelerators, the few we shall con- 



sider are the ones commonly used, 
namely : 

Litharge, Lime. 

White lead, Magnesia calcined, 

Sublimated white Magnesia c a r b o- 

lead, uate, 

Red lead, Magnesite. 

Under the third class, fillers, we 
shall discuss substances which, as the 
name implies, may be obtained on 
the market at a price to enable the 
manufacturer to use them in large 
quantities, substances which chem- 
ically are more or less inert, such as 
Barytes, Kaolin. China Clay. 

Alumina oxide, Talc, Sbapstone, 

Aluminum Flake, Fossil Flour, 
Whiting, Asbestos, 

Clays, Blue Lead, 

Silica (Atmoid), Magnesite. 

There are several more which 
might be classified here but seem bet- 
ter to appear in the fourth group, 
pigments : 

White Pigments 
Zinc white, Barium sulphate. 

Lithopone. Barytes. 

Zinc sulphide. Kaolin. 

Red or Brown Pigments 
Antimony Crimson. Vermilion, 
Antimony Golden. Venetian Red, 
Rouge. Indian Red. 

Red Ochre. 

Black Pigments 
Lamp Black. Graphite. 

Bone Black, Lead sulphide. 

Hydrocarbon, 

Yellow Pigments 
Yellow Ochre. . Cadmium sulphide. 

Chrome Yellow, Arsenic sulphide. 

Green Pigments 
Chrome Green. Rinmann's Green. 

Ultramarine Green, 

Blue Pigments 
Ultramarine Blue. Prussian Blue, 
Thenard's Blue, Chrome Blue. 

Above are the substances which 
will be dealt with in this chapter. 
Sulphur 

The substance, sulphur, with which 
every man in a rubber factory is ac- 



71 



RUBBER MANUFACTURE 



quainted,. was also known to the 
ancients, for Homer 900 B.C. re- 
corded that it was used in medicine 
and in fumigation. In 800, Gebir 
put forth the idea that all metals 
were compounds of sulphur and mer- 
cury and that it was possible to 
change from one metal to another by 
changing the ratio between these two 
substances. Lavoisier was the first 
to recognize it as an element. 

The use of sulphur in rubber, how- 
ever, remained a secret until Good- 
year, in 1839, and Hancock indepen- 
dently in 1844, showed its effect upon 
rubber when heated in contact with 
it. 

This element occurs in many dif- 
ferent ways in nature and is well dis- 
tributed over the earth. It is found 
in the free state in large quantities 
in Sicily and Louisiana. It occurs 
in the f orm of sulphides of the metals 
like iron, copper, lead and zinc; in 
the form of hydrogen sulphide in cer- 
tain springs; as sulphur dioxide is- 
suing from volcanoes; as sulphates 
of many elements like lead, barium, 
calcium, and strontium ; then in or- 
ganic substances like albumen, horn, 
etc. We must realize, therefore, the 
great distribution of this element in 
nature. 

It has been estimated that the de- 
posits of sulphur in Sicily, still un- 
touched, contain fifty-five million 
tons, and that it will require about 
one hundred years to exhaust them. 
"Up to the year 1900, it is claimed 
that 95 per cent of the world's pro- 
duction of sulphur came from Sicily, 
but in 1908, the United States pro- 
duced 45 per cent of that amount, 
and from that date has continued to 
produce more and more. 

Just a few words in regard to the 
methods used in Sicily and the 
United States for obtaining sul- 
phur. In Sicily, the sulphur is found 
from 150 to 600 feet below the sur- 
face of the earth. It is reached by 
inclined winding shafts. In earlier 
times, all of the sulphur was brought 
to the surface upon the backs of men, 
women, and children, but modern 
methods of mining are in general use 
there .how, and it is raised by me- 
chanical means. 



The ore is first graded into rich, 
good and ordinary lots. These ores 
were formerly made into piles and 
then fire was set to the piles. As 
part of the sulphur burned, its heat 
of combustion would melt the re- 
mainder, which would run down 
through the pile and collect in a 
trench around the original heap. This 
method, of course, caused a great 
loss, and in addition, the vapors of 
sulphur dioxide damaged the health 
of the people and killed the vegeta- 
tion for miles around. By this method 
only about 25 per cent of the sul- 
phur was actually obtained. 

Next in line of advancement came 
the method of building larger heaps 
of ore and covering them over with 
earth, just leaving here and there 
shafts through the heap. Wood was 
placed in these shafts and kindled. 
Some of the sulphur would burn and 
thus melt the remainder, which was 
collected. These piles would re- 
quire from one to two months to 
burn out. From these as high as 60 
per cent of sulphur was obtained. 

The next improvement came in 
1880, when Gill proposed his regene- 
rative furnace. He constructed two 
large brick chambers, which com- 
municated with the same chimney 
so that while one was burning, the 
other might be in the process of 
charging. The combustion here could 
be more perfectly regulated, and as 
these chambers had a double bot- 
tom, thus separating the ore from the 
collected sulphur, a decided advance 
was made. As high as 75 per cent of 
the sulphur was obtained by this 
method. 

The next great improvement came 
in 1891, when the removing of the 
sulphur from the ore was effected by 
the use of superheated steam. This 
was accomplished by building hori- 
zontal iron cylinders, equipped with 
a tight-fitting door and a track which 
would allow small iron cars, with 
perforated bottoms, containing the 
ore, to be run into this dram. The 
door is closed and steam at 130 deg. 
C. admitted, when the sulphur melts, 
runs to the bottom of the drum, 
which is slightly inclined, and then 
into a well which serves as a recep- 



THE MANUFACTURE AND USE OF INORGANIC FILLERS 



tacle for the molten sulphur. This 
process is rapid, gives from 80 per 
cent to 90 per cent of the total sul- 
phur, and does away with the objec- 
tionable sulphur dioxide fumes of 
the former methods. 

All of these methods produce crude 
sulphur and this must then be re- 
fined. This refining process is ac- 
complished by heating the crude sul- 
phur in retorts and distilling it and 
condensing it in large chambers. If 
the temperature of these condensing 
chambers is above 114 deg. C, then 
liquid sulphur is obtained, which is 
drawn off into molds and known as 
brimstone. If the temperature is 
maintained below 100 deg. C, then 
flowers of sulphur will collect. 

The deposits of sulphur in Louisi- 
ana occur about 1000 ft. below the 
surface of the ground. The method 
of obtaining this sulphur was sug- 
gested by Frasch. He drilled a well, 
similar to that used for extracting 
petroleum from the earth, then into 
this casing, he imposed three other 
concentric tubes, lined with alumi- 
num, which would not be attacked by 
the sulphur. Superheated water was 
forced down through the outer pipe. 
"When it came in contact with the sul- 
phur, the latter melted, and was 
forced part way up the inner tube. 

To bring it the remainder of the 
distance, aluminum pumps were tried 
but were not strong enough to sup- 
port the strokes of. the piston. The 
difficulty was then overcome by forc- 
ing air down the inner tube which 
emulsified the sulphur, thus making 
it very light and it rose to the sur- 
face. Here it was collected in large 
wooden boxes where it solidified. 

By simply melting this sulphur 
again in iron boilers by use of steam 
and drawing it off into suitable 
molds, a sulphur of higher than 97 
per cent is obtained. It is estimated 
that the Louisiana deposits contain 
at least forty million tons of sulphur. 

Sulphur exists in three forms. 
The most stable is the rhombic 
variety which has a specific gravity 
2.06 and melts at 114.5 deg. C. The 
monoclinic is next in stability and 
has a specific gravity of 1.92. Above 
95 deg. C, the rhombic changes into 



monoclinic and vice versa. If boiling 
sulphur at a temperature of 445 deg. 
C. is poured into water, there re- 
sults a form devoid of crystalline 
structure and called amorphous, or 
plastic sulphur. It resembles rubber 
in many of its physical properties 
but soon changes back into the 
rhombic variety. Therefore when 
sulphur is added to rubber and vul- 
canized at 45 lbs. pressure of steam 
that is equivalent to a temperature 
of 145 deg. C. and our sulphur must 
be above the temperature at which 
rhombic exists and in fact approach- 
ing the temperature • at which the 
amorphous exists. 

Rhombic sulphur exists in two 
modifications, roll sulphur or brim- 
stone and flowers or flour of sulphur. 
It is the latter modification which is 
largely used in the rubber industry. 
In some places, they grind brim- 
stone, sift it, and it gives equally as 
good results. 

The flowers of sulphur results from 
the sublimation of sulphur as was 
pointed out above. Its specific 
gravity runs about 2.0 and it con- 
tains some modifications which are 
insoluble in carbon bisulphide. 

It always contains some free sul- 
phuric acid due to its slow oxidation. 
The sulphur should be examined from 
time to time to ascertain the amount 
of free acid, which should not show 
more than 0.2 per cent calculated as 
H 2 S0 4 . It should contain practically 
no ash, in fact the presence of any 
suggests adulteration, generally with 
an infusorial earth. . 

Sulphur is sometimes used in sul- 
phur baths into which forms to be 
vulcanized are dipped, and here it 
serves simply as a heat carrier in the 
place of the more usual steam pres- 
sure or hot air. 

Sulphur monochloride, S 2 C1 2 , was 
found to have the property of com- 
bining with rubber to produce a sub- 
stance resembling the sulphur vul- 
canized rubber. It has the power of 
entering into this chemical union at 
ordinary temperature, thus we have 
by its use what is known as the ' ' cold 
cure " process. 

It is made by passing dry chlorine 
gas over molten sulphur, when the 



RUBBER MANUFACTURE 



two elements combine in the ratio of 
SoCL. It distills out of the appa- 
ratus and is condensed as a reddish 
yellow liquid with a boiling point of 
138 deg. C and a specific gravity of 
1.69. Moisture decomposes it in the 
following manner. 

2 S 2 C1 2 + 2 HOH-> 

S0 2 + 3 S + 4 HC1 

Therefore when it is used in the 
rubber industry, moisture must be 
excluded as far as possible. 

Sulphur is readily soluble in the 
monochloride and the monochloride 
is likewise converted into the di- 
chloride by treating it with an excess 
of chlorine. So when examining the 
monochloride, we necessarily look for 
these two substances, sulphur and 
sulphur dichloride as impurities. 
The presence of these affects the boil- 
ing point of the monochloride and 
that gives us a very easy method of 
ascertaining the relative purity of 
our material. In commercial work, 
a range in boiling point from 130 
deg. to 140 deg. C is allowed. 

The dichloride has a boiling point 
of 64 deg. C, and it is a very ob- 
jectionable impurity in any amount. 
The dissolved sulphur may run as 
high as 5 per cent. If more than this 
is present, the cured article will 
" bloom " or " sulphur up." This 
is determined by distilling off the 
chloride and extracting the residue 
with carbon disulphide, which dis- 
solves the sulphur, placing the solu- 
tion in a tarred flask, evaporating 
the solvent off and drying at 110 deg. 
C, when the sulphur remains and is 
determined. 

Pure sulphur chloride should con- 
tain 52.5 per cent of chlorine. It is 
generally used for vulcanizing proc- 
esses in a dilute solution of carbon 
bisulphide or carbon tetrachloride 
and the articles to be cured are 
dipped into this solution. The action 
is only a surface action and there- 
fore may be used only with thin 
articles. In some cases the articles 
to be cured are subjected to the 
vapors of sulphur chloride when the 
desired reaction takes place and a 
glossy surface is produced. It finds 
extensive use in the manufacture of 



rubber substitutes. Its use here 
will be discussed at greater length 
in a chapter which follows and which 
deals entirely with -the question of 
"substitutes." 

Because of the use of carbon bisul- 
phide and carbon tetrachloride in 
the " cold cure," it seems perhaps 
wise to devote a little space here in 
considering these substances. 

Carbon bisulphide, like the chlor- 
ide of sulphur, is made by the direct 
union of the elements. The appa- 
ratus for effecting this action con- 
sists of a tall, heavy walled cast-iron 
retort which is filled with carbon, 
generally coke, and heated to red 
heat. At the bottom of this retort, 
there enters a slow stream of molten 
sulphur which, coming into the re- 
tort, immediately changes into vapor 
and then combines with the carbon 
forming the bisulphide. This at the 
temperature of the retort is a gas 
and thus passes out the top into a 
system of condensers which first re- 
move from the bisulphide any sul- 
phur vapors which may have been 
carried along with it; then into a 
water condenser which condenses the 
bisulphide. 

This is of course the crude product 
and for the majority of cases must 
be purified. This is done by adding 
to it a little lime water and shaking 
it, then placing it in a still with 
about a 1 per cent solution oil, a lit- 
tle water and some lead acetate. 
When the bisulphide is distilled out, 
it will represent a fairly good grade. 

This substance is used very exten- 
sively outside the rubber industry. 
Up to 1850, however, practically its 
only use was in connection with the 
rubber industry, and then as to-day 
it was used as a diluent in the cold 
cure process, and as a solvent for 
rubber, hence coming its use in the 
preparation of rubber cements. 

It boils at 46 deg. to 47 deg. C, 
and has a specific gravity of 1.27. It 
generally contains some dissolved 
sulphur, which may be determined 
by distilling 100 c.c. out of a tared 
flask. It should show at most two 
grams of distillation residue per 
liter. Having such a low boiling point, 



THE MANUFACTURE AND USE OF INORGANIC FILLERS 



75 



it evaporates very rapidly and with 
the air, forms a very inflammable 
mixture often causing bad fires. Its 
vapors are also poisonous and may 
produce serious results upon the 
workmen. The tetrachloride of car- 
bon is made by passing dry chlorine 
through CS 2 in which contains a little 
iodine and a catalyst of asbestos im- 
pregnated with magnesium chloride 
is suspended. The reaction takes 
place as follows : 

CS 2 -f 3 Cl 2 ~> CC1 4 + S, Cl 2 

These two products may be sep- 
arated by distillation, but it has been 
found that in the presence of a little 
powdered iron, the following reac- 
tion? will take place : 

CS 2 + 2 S 2 Cl 2 ~> CC1 4 + 6 S 

These resulting products are sep- 
arated by distillation and the sul- 
phur is used to produce carbon bi- 
sulphide again. 

The tetrachloride is purified by 
washing with a solution of caustic 
soda and then distilling from a so- 
lution of calcium hypochlorite. It 
boils at 77 deg. C. and has a specific 
gravity of 1.63. It is an excellent 
solvent for fats and resins and has 
the great advantage of not being in- 
flammable. It even has the power 
of rendering certain inflammable 
solvents uninflammable when it is 
added to them. Its great use in the 
rubber industry is that it is mixed 
with coal tar naphtha and will pro- 
duce non-inflammable rubber solu- 
tions, and likewise its use as a dilu- 
ent in the cold cure process. 

To test the commercial variety of 
the tetrachloride, it should distill be- 
tween 75 deg. and 78 deg. C. and 
leave no residue. The determina- 
tion of its specific gravity will gen- 
erally reveal the presence of any 
adidterants. 

Inorganic Accelerators 

The second group of materials we 
called inorganic accelerators or ' ' sul- 
phur carriers " as they have some- 
times been called. The theories ad- 
vanced in explanation of their action 
in hastening vulcanization will be re- 
served for the chapter dealing with 
the theories of vulcanization. 



The one which has been used to 
greatest extent is probably litharge, 
the monoxide of lead. It is made by 
heating the metal lead in a reverber- 
atory furnace with a current of air 
passing over it. It requires some 
time for the oxidation to be complete 
and must also be watched that some 
of the other oxides of lead are not 
formed. The yellow powder formed 
in the above process is called Mas- 
sicot. When this is melted and then 
allowed to cool rapidly, the mass 
which results is called litharge. It 
has a specific gravity of from 9.2 to 
9.5. Considerable litharge is also 
made to-day in connection with the 
refining of silver. The lead is re- 
moved from the molten silver when 
it is oxidized with a current of air 
to the monoxide. It then floats on 
the surface of the silver and is re- 
moved. 

Litharge is generally supplied in 
a high state of chemical purity, but 
varies considerably in degree of fine- 
ness and this of course has an in- 
fluence upon its color. Litharge is 
slightly basic and therefore tends 
to absorb carbon dioxide, which is ob- 
jectionable. A sample should there- 
fore dissolve in dilute nitric acid 
without any effervescence, and with- 
out leaving a residue of the dark 
colored lead peroxide, which is very 
objectionable. 

It may contain some unoxidized 
metal, which does no harm and may 
be detected by dissolving the litharge 
in acetic acid instead of nitric. It 
is always well to test the resulting 
solution for copper as that is ob- 
jectionable even in small amounts. 

Litharge might well be classed 
under the heading of Black Pigments 
as it imparts that color to the vul- 
canized rubber due to the forma- 
tion of its sulphide. Until recently, 
nearly all of the black and dark gray 
rubbers were colored with litharge 
but at present it is used largely on 
account of its accelerating action 
upon vulcanization. 

White lead is a basic carbonate of 
lead and has an accelerating action 
upon the rate of cure but to a less 
degree than litharge. As a pigment, 
it does not possess the coloring power 



RUBBER MANUFACTURE 



which litharge has. It gives the 
article more of a bluish gray color. 

It is made by several different 
methods, some requiring a long 
period of time, others proceeding 
more rapidly. From the white 
lead manufacturer's point of view, 
the rapid method is naturally the one 
to be preferred, but from the con- 
sumer's viewpoint, the products of 
the slow process seem to be desired 
most. 

The Old Dutch Process consists in 
subjecting lead plates to the action 
of acetic acid and carbon dioxide 
formed by fermentation. This first 
produces the acetate of lead, then the 
basic acetate, and finally after a lapse 
of five or six weeks, the basic car- 
bonate, a white lead, results. The 
white lead is freed from any un- 
affected lead or acetate by washing 
with water. The Germans have a 
quicker method where they blow 
steam and acetic acid vapors into 
chambers containing lead plates and 
then bring into these same chambers 
carbon dioxide from a coke furnace 
and the basic carbonate of lead re- 
sults. It is washed and dried, and 
ready for market. 

The French dissolve litharge in 
acetic acid forming the basic acetate 
and then pass carbon dioxide through 
this until the white lead formed, 
which settles to the bottom, is trans- 
ferred to a filter press, dried and 
ground. 

The Russian white lead is made by 
producing the neutral lead carbon- 
ate by the action of carbon dioxide 
upon the basic acetate of lead. The 
neutral carbonate is then made into 
a paste with water, about 1 per cent 
of lead acetate added, and also 30 
per cent of lead oxide. The whole 
mass is stirred in the cold with the 
addition of a little water until it all 
hardens. In from three to four 
hours, the process is complete and a 
fine grade of white lead results. 

There is a method whereby the 
freshly precipitated lead sulphate is 
converted into the basic sulphate by 
heating with caustic soda, then when 
this solution is heated with sodium 
carbonate, the white lead is pre- 



cipitated. In this country, atomized 
lead is produced by blowing a jet of 
steam against small holes where 
molten lead is issuing. This " lead 
sand " is then treated with dilute 
acetic acid for about seven days, 
while air, carbon dioxide, and a little 
steam are blowing through the vats. 
White lead results which is washed 
from the unaltered lead. 

The water of hydration which 
may be present in white lead often 
causes " blowing." It has a specific 
gravity of 6.1 to 6.2. 

Sublimed white lead is not what 
the name implies, a carbonate of lead, 
but is a basic sulphate. Its use is in- 
creasing in favor as it does not tend 
to produce " blowing." It acceler- 
ates more than white lead, and pro- 
duces a black product when vulcan- 
ized. It is a velvety powder and 
mixes readily with the rubber. It 
has a slightly higher density than 
white lead. 

Bed lead, or minium, is the tetrox- 
ide of lead, or really it may be 
thought of as a mixture of lead mon- 
oxide and dioxide. 
2 PbO + Pb0 2 ~> Pb 3 4 (Red Lead) 

It is made by heating litharge in 
a reverberatory furnace at a tem- 
perature of 450 deg. C, but must not 
be allowed to melt. The best grade 
is made by heating the monoxide of 
lead with sodium nitrate in an oxidiz- 
ing flame to a dark red heat. It has 
a specific gravity of 8.6 to 9. It is 
one of the most powerful inorganic 
accelerators, perhaps due to the heat 
of reaction between it and the sul- 
phur. It is used in rapid curing 
stocks. It can be used only within 
certain limits as it will attack the 
rubber as a result of its strong oxidiz- 
ing power. 

The adulterants that must be 
looked for are calcium carbonate, 
barytes and ferric oxide. 

Under the term " Lime," we 
largely, in connection with rubber, 
refer to the hydroxide of calcium 
which is " slaked lime," in contrast 
to ' ' quick " or " burnt lime ' ' which 
is the oxide of calcium. The latter is 
made by heating limestone, which 
is calcium carbonate, in kilns to a 



THE MANUFACTURE AND USE OF INORGANIC FILLERS 



temperature of 1,000 cleg, when it 
loses its carbon dioxide and quick 
lime results. When this is mixed 
with about one-third of its weight of 
water, the white, powdery, swollen 
mass of slaked lime results. If more 
water is added, the soluble alkalies 
are washed out and a softer powder 
will result. It has a specific gravity 
of 2.1 and has a finer grain than 
the quick lime. It is added only in 
small proportions. 

In small quantities, it takes up the 
moisture which may be present in a 
stock and thus prevents blowing. It 
has the power of combining with the 
free sulphur and thus tends to pre- 
vent " blooming." Excess of lime 
tends to diminish the resiliency of 
rubber and also makes it harder, hav- 
ing that effect even in hard rubber 
articles. It also has an accelerating 
action upon the rate of cure. 

Lime should be fairly free from 
carbonate and silica and upon igni- 
tion show close limits to that ■ of 
Ca (OH),, that is, 24.3 per cent. 
Manganese is sometimes present in 
lime and renders it useless for the 
rubber manufacturer. It affects rub- 
ber in the same manner as copper 
does. 

There are several forms of mag- 
nesium compounds in use. We have 
two kinds of calcined magnesia 
(which is the oxide), known as 
" heavy " and " light " calcined. 

If to a hot solution of a mag- 
nesium salt, a hot solution of soda 
is added, there will be formed what 
is known as heavy magnesium car- 
bonate and when this is calcined, the 
heavy magnesia results. If, on the 
contrary, cold solutions are used, the 
light carbonate will be formed, and 
when this is calcined the light mag- 
nesia results. The only difference 
therefore is in the structure of the 
two. 

It is used in the same manner as 
lime. Its specific gravity is 3.2 to 
3.6 and it is a little coarser grained. 
It possesses marked accelerating 
power upon the rate of cure and also 
increases the toughness of the prod- 
uct more than 10 per cent except 
in rapidly curing stocks. 



The magnesias suffer varying igni- 
tion losses ranging from 2 to 20 per 
cent. When a compound has been 
made up with a certain grade of 
magnesia, then deliveries which fol- 
low should not be allowed to vary 
much from the ignition loss of the 
original. Rubbers running high in 
resins seem to give better results 
when compounded with magnesia. 

There occurs in nature the mineral, 
magnesite, which is the carbonate of 
magnesium, of sufficient purity that 
it may be used in compounding. The 
carbonate is also artificially made as 
pointed out above. 

These substances possess very little 
accelerating power, and are used 
largely as fillers. As fillers they may 
be employed up to 30 per cent with- 
out seriously injuring the rubber. 

Under the third division of oui 
subject, fillers will be considered in 
the meaning which the word itself 
implies : substances which are not 
used on account of any good prop- 
erty which they impart to the rubber, 
nor on account of any color which 
they may produce in the finished prod- 
uct. In other words, they are cheap 
materials which to a certain extent 
may be used in the place of more ex- 
pensive substances. Their amount is 
regulated by experiment so that too 
much will not be used and thus im- 
pair the finished product. 
Barytes 

The first one of these for considera- 
tion will be barytes, or heavy spar. 
It is found in nature in a compara- 
tively pure form, in fact, in so high 
a degree of purity that it needs no 
other preparation than that of grind- 
ing to a fine powder. It may be 
found in shades varying from a good 
white to a gray, depending upon the 
per cent of barium sulphate present. 

It is obtained also by artificial 
means. First, the mineral or natural 
sulphate is heated in a furnace with 
carbon when there results the sul- 
phide and oxide of barium. These 
are then dissolved in water and so- 
dium sulphate added and the insolu- 
ble artificial barium sulphate, barytes, 
is precipitated. 

Second, it is made by dissolving 



78 



RUBBER MANUFACTURE 



the mineral erite. which is the car- 
bonate of barium, in hydrochloric 
acid, and then adding sodium sul- 
phate, when the barium sulphate re- 
sults. 

It has a specific gravity of 4.5 to 
4.6 and is obtained very often under 
the name of " permanent white " or 
" blanc fixe." Due to its high spe- 
cific gravity, it is employed to in- 
crease the specific gravity of some 
stocks. The artificial product is to be 
preferred to the natural one as it is 
amorphous while the ground mineral, 
even though it is reduced to a fine 
powder, still retains more or less its 
crystalline structure. It is used to 
adulterate white lead, and to a cer- 
tain extent, has the advantage of not 
being effected by hydrogen sulphide 
or metallic sulphides.' 

Aluminum Compounds 

There are several compounds of 
aluminum which are used as inert 
fillers. 

" Aluminum flake " is a natural 
product coming in several different 
colors from white to gray and gray to 
brown. It has a specific gravity of 
2.5 to 2.6 and is used to a certain ex- 
tent in place of zinc oxide. 

Aluminum oxide does occur in na- 
ture but the artificial product is the 
one desired for use in rubber. In the 
Bayer process the mineral bauxite 
is calcined and pulverized, mixed 
with a little lime and then treated 
with sodium hydroxide solution of 45 
de. Be, at a pressure of three to four 
atmospheres. Sodium aluminate re- 
sults which is soluble in water. It is 
then filtered hot and, after suitable 
dilution, pure gelatinous aluminum 
hydroxide is added. It is then agi- 
tated for from five to six days when 
all of the aluminum is precipitated 
both from the bauxite solution and 
from that which was added. It is 
then recovered by a filter press, and 
thoroughly dried, when a fine white 
powder results with a specific gravity 
of about 3.9. It was with the use 
of this oxide that Eaton suggested the 
making of a pure white rubber. 

The hydroxide of alumina is now 
coming into use in some factories. It 
is one o£ the lightest gravity materials 
possible to obtain. 



Kaolin, or China clay, is a natural 
occurring product. In chemical com- 
position it is a hydrated silicate of 
alumina. It acts as an inert filler in 
all the rubber compounds. It has a 
specific gravity of 2.3 to 2.6. It 
should show an ignition loss of 11 to 
14 per cent and should not be at- 
tacked by dilute acids. It often runs 
very high in moisture which, of 
course, must be guarded against. 

Talc 

Talc is a silicate of magnesia oc- 
curring native in the earth in a suffi- 
ciently high state of purity so that it 
may be reduced to a powder and used 
directly in the industries. It is not 
used to any great extent in rubber 
stocks but is employed a great deal 
in all kinds of work to prevent sur- 
faces from sticking together. Molds 
are dusted over with it to keep the 
rubber from adhering to them dur- 
ing vulcanization. Some goods are 
buried in it during vulcanization. 

Talc has a specific gravity of 2.7. 
When it is used in compounding, it 
imparts to the rubber, smoothness 
and stiffness, and also increases elec- 
trical insulation when used in cable 
coverings. A common adulterant is 
calcium carbonate, which is detected 
by the effervescence when treated 
with an acid. 

Soapstone is really a form of talc 
and as such, is used in large quanti- 
ties. . 

Silicon Oxides 

There are other materials on the 
market under different names which 
are in reality the same from a chem- 
ical point of view. Silica, Atmoid, 
Infusorial Earth, Fossil Flour and 
Mountain Flour are all names given 
to the oxide of silicon. This mate- 
rial occurs in a great many different 
forms in nature. All forms are with- 
out material effect upon rubber com- 
pounds, other than stiffening the 
product to some extent. They have 
a low specific gravity ranging between 
2.7 and 2.9. 

These materials consist of the skele- 
tons of microscopic animals. Large 
deposits are found in Nova Scotia 
and Germanv. 



THE MANUFACTURE AND USE OF INORGANIC FILLERS 



Asbestos 

Asbestos is a silicate of magnesia 
with a varying amount of the mag- 
nesia replaced by lime, together with 
ferrous oxide and alumina. Large 
deposits of it are found in Italy, 
Canada and Cape of Good Hope. It 
is used both as fiber and as powder. 
The fibrous form is used in mechan- 
ical goods for it increases the tough- 
ness and unyielding quality of the 
structure. It is used in goods that 
are subjected to a high temperature 
and also in articles like brake blocks. 

Calcium Carbonates 

Chalk or whiting is the carbonate 
of calcium. It occurs in nature in 
several modifications, as limestone, 
chalk, and marble. The chalk deposits 
are the remains of microscopic 
marine animals. Chalk is obtained 
in a fine white grade. 

Whiting is really purified chalk, 
made by grinding the chalk, then 
floating it and the fine white sediment 
is obtained by running it through a 
filter press. It is then dried rapidly. 
If, during the drying, too high a tem- 
perature is used, the product will 
feel harsh. As it is slightly deliques- 
cent it must be kept in a dry place ; 
otherwise it may cause trouble in the 
stock where it is used. 

Large quantities of whiting are 
used in the rubber business on ac- 
count of its cheapness. It has a spe- 
cific gravity of 2.7 to 2.9. It will 
increase the i*esiliency of rubber and 
also increase its hardness without 
producing the " stony " effect that 
other ingredients do. 

Sulphides 

We find in nature mineral deposits 
of the two sulphides of lead and zinc. 
If such ore is smelted with a mixture 
of coal and lime, it produces what is 
known as Blue Lead. It is an ex- 
tremely fine powder and possesses a 
high specific gravity. It is a cheap 
product and, to a certain degree, hast- 
ens the rate of cure in the stocks 
where it is used. Therefore, it may 
be used in the place of litharge and 
will also produce the fine black prod- 
uct. 

Magnesium Carbonate 

Magnesium carbonate, which was 



mentioned under the first class, is also 
used as a filler. 

White Pigment 
Under our third group, White 
Pigments, may be discussed materials 
which might have been grouped 
under fillers. This will be true of all 
the divisions which follow. 

Zinc Oxide 

The first and most important of the 
white pigments is zinc oxide. No one 
pigment is used as extensively as this 
one in the manufacture of white rub- 
ber goods. 

It may be made by roasting any one 
of the zinc ores, but the best method 
is that of burning the pure metal. The 
trouble with roasting the ores lies in 
the fact that lead, iron, and copper 
are very often present in these and 
thus will be found in the finished 
product. 

A good sample of zinc oxide should 
dissolve completely without effervesc- 
ing in a 10 per cent solution of acetic 
acid. If it is desired to test for the 
presence of iron, lead or copper, in 
the oxide, all that is necessary to do 
is to dissolve the specimen in dilute 
hydrochloric acid, and conduct hy- 
drogen sulphide into it. If it is free 
from the above metals, there will be 
no preciptate formed. 

Inferior grades of zinc are often 
adulterated with barytes, whiting, or 
kaolin and the presence of these will 
be detected when the sample is 
treated with acetic acid. The barytes 
and kaolin are both insoluble and the 
whiting will produce the effervesc- 
ence. White lead is sometimes an 
adulterant. 

Zinc oxide has a specific gravity of 
5.5 to 5.6. Although it is one of the 
extensively used white pigments, yet 
it is not all that is to be desired. Its 
covering power is only moderate and 
during vulcanization, it turns to a 
yellow color. The higher the tem- 
perature and longer the period of 
vulcanization, the more pronounced 
this color becomes. 

Another defect of zinc oxide is the 
fact that dilute acids will dissolve it 
out of the vulcanized rubber goods. 
As a result of this, certain countries 
prohibit its use in rubber articles 



80 



RUBBER MANUFACTURE 



which come in contact with foods or 
beverages in their preparation. 
Zinc Sulphide 

A white pigment which has in- 
creased in favor rapidly is zinc sul- 
phide. It occurs in nature in the 
mineral known as zinc blende, but 
the product used in rubber is an arti- 
ficial one. It may be produced by 
causing zinc dust and vapors of sul- 
phur to come together at an elevated 
temperature. It may also be pro- 
duced by precipitating it from a solu- 
tion of zinc with ammonium sulphide. 

It is a white powder with a specific 
gravity of 3.3 and possesses greater 
covering power than the oxide. It 
has the distinct advantage of not 
changing to the yellow tint during 
vulcanization, and it is not leached 
out of the rubber by dilute acids as is 
the oxide. It is liable to the same 
adulterations as the oxide is plus the 
oxide itself. The best grades of zinc 
sulphide should run as high as 90 
per cent, purity. 

A very good method of determining 
its purity is to place about 0.2 of a gram 
of the dried material in a flask and 
shake it up with 50 c.c. of N/10 iodine 
solution. Five c.c. of concentrated 
hydrochloric acid are then added and 
the whole is allowed to stand a couple 
of hours with occasional shaking. 
By this, time, all of the white par- 
ticles should have disappeared and 
the excess iodine is then titrated with 
sodium thiosulphate solution. Each 
c.c. of the iodine solution which re- 
acted with the hydrogen sulphide, 
produced when the acid was added to 
the zinc sulphide, is equivalent to 
0.00485 grams of the sulphide. Tims 
its purity is easily calculated. 

Lithopone 

Another zinc pigment which was 
first used in paint and now exten- 
sively in rubber, is one known as 
lithopone. It is an artificial prod- 
uct, made by bringing together solu- 
tions of barium sulphide and zinc sul- 
phate, when the following reaction 
takes place : 

Ba S 4- Zn SO, ->Ba S0 4 +ZnS* 

The resulting product is insol- 
uble and is a compound of zinc sul- 



phide and barium sulphate which is 
known as lithopone. It has a specific 
gravity of 3.8 to 4.2 and should con- 
tain 70.5 per cent of barium sulphate 
and 29.5 per cent of zinc sulphide. It 
varies considerably, however, from 
these per cents, depending upon the 
method of preparation. 

Of course, the valuable part of it 
is due to the zinc sulphide and there 
is a standard grade of lithopone, 
known as " Blue Seal," which is 
guaranteed to have 30 per cent of 
zinc sulphide. For general purposes 
it is necessary only to examine a sam- 
ple for moisture, acid insoluble, and 
sulphide. 

The acid insoluble is determined by 
boiling one gram of the dried sample 
with concentrated hydrochloric acid, 
diluting and boiling again and then 
filtering, drying and igniting the 
residue in a platinum crucible, and 
then weighing. This residue should 
not exceed 70 per cent. 

To detect the presence of kaolin as 
an adulterant, a little hydrofluoric 
acid may be added to the residue, 
evaporated off, and reweighed, and 
any loss in weight represents the 
presence of silicates. 

What was said in regard to the use 
of zinc sulphide may be said of litho- 
pone. 

Baryles and Kaolin 

In addition to these white pig- 
ments, may be mentioned barytes and 
kaolin, which v/ere considered under 
fillers. 

Red Pigments 

The next class of pigments for our 
consideration are those which impart 
a red color to rubber goods. 

Golden and Crimson Antimony 

The first to be mentioned are Anti- 
mony Golden and Crimson, and these 
two are divided into grades accord- 
ing to color, for instance, Golden 
No. 1, Golden No. 2. 

The Crimson Antimony is little 
used by itself but is made by boiling 
together antimony trichloride and 
thiosulphate solutions, when the tri- 
sulphide of antimony is precipitated. 

Colors varying from this crimson 
to orange are then produced, the 



THE MANUFACTURE AND USE OF INORGANIC FILLERS 



shade depending upon the conditions 
of precipitation or upon the respec- 
tive percentages of crimson and 
golden sulphides in the mixtures. 

The golden sulphides are the ones 
in commonest use. These are made 
by boiling powdered stribnite, which 
is the mineral containing the natural 
•sulphide of antimony, with alkaline 
polysulphides when there results sulf- 
antimonate in solution. When this 
sulfantimonate is treated with hydro- 
chloric acid there will be precipitated 
a mixture of the sulphides of anti- 
mony and also some free sulphur re- 
sulting from the polysulphides. 

One form of the orange antimony 
is co-precipitated with hydrated cal- 
ch5ni sulphate and is called " plas- 
tered antimony." This grade, of 
course, is cheaper and does not con- 
tain as high a percentage of the red 
pigment. 

When it comes to determining the 
true worth of a sample of antimony, 
the best method is to subject it to 
actual vulcanization experiments, be : 
cause it is found that some antimonies 
will not hold their color during vul- 
canization. This fact cannot be ascer- 
tained by chemical tests. 

In analysis the following deter- 
minations are generally made : mois- 
ture, free sulphur, antimony, calcium 
sulphate, sulphide-sulphur. 

The free sulphur present is what 
led many to believe for a long time 
that antimony red was a vulcanizing 
agent. In fact, even now some manu- 
facturers claim that they obtain bet- 
ter results if they mix the sulphur 
into the antimony which they use in 
the compound. To supply such a de- 
mand the producers of sulphureted 
antimony put free sulphur into it up 
to the extent in certain cases of 40 
per cent. It is determined by extract- 
ing a weighed amount of antimony in 
a Soxhlet extractor with carbon disul- 
phide or acetone for about eight 
hours. The solvent is evaporated and 
the amount of free sulphur calcu- 
lated. 

The antimony itself, iron and cal- 
cium sulphate are determined in the 
usual manner. The sulphide sulphur 
is calculated by determining the total 
sulphur in the extracted sample and 



subtracting from this the sulphur 
present in the sulphate. 

In connection with the use of the 
sulphides of antimony, we shall pub- 
lish some of its merits as put forth 
by a prominent manufacturer : 

" First — Antimony Sulplmret vised in 
the curing of rubber acts as a sulphur 
carrier causing all of its free sulphur to 
unite with the rubber. Sulphur added as 
a sulplmret is taken up completely by the 
rubber. Therefore it is not necessary to 
add an excess of sulphur. 

" Second — On account of the above, 
'blooming' does not take, place for prac- 
tically none of the sulphur is left uncom- 
bined in the rubber. 

"Third — On account of the above, vul- 
canization can be carried on at a lower 
temperature; thus the tendency to over- 
cure is diminished. 

"Fourth — On account of the above, (he 
rubber has a longer life. It can be kept 
much longer than gray rubber before it 
will begin to deteriorate. 

"Fifth — It has more elasticity. This is 
shown by the following test : A piece of 
red rubber tubing and a piece of gray 
tubing are bent firmly and pressed with a 
spring clothespin clip. The two samples 
are allowed to stand in the sunlight for 
several days when the clips are removed. 
It will be noted that the properly anti- 
mony-cured red tube will spring back into 
its original shape immediately upon re- 
moval of the clamp. The gray tube goes 
back into its old form slowly. In use this 
is noticed when a tire goes flat over night. 
The red tube allowed to bend by the 
weight of the car will immediately spring 
back into place when the weight is re- 
moved. The gray tube will remain bent 
even after the weight of the car is lifted. 

" In a large lot of returned shelf goods, 
half gray and half red, the following was 
noticed. The gray tubes when' removed 
from the cartons were in bad shape. They 
could not very well be unfolded as their 
creases seemed to be permanent. The red 
ones, however, were in just as good shape 
as the day when they left the plant more 
than a year before and they were simply 
transferred to new cartons and placed on 
sale. The gray tubes were covered over 
with a thick coating of sulphur bloom 
while the red ones were entirely free from 
bloom. The superintendent of the plant 
pointed out the fact that the only differ- 
ence between the two stocks was that the 
gray Ones had obtained all of their sul- 
phur from sulphur flour while the red 
ones obtained the larger part of their sul- 
phur from antimony sulplmret." 

Due to the oxidization of the sul- 
phur, we find that most samples con- 
tain free sulphuric acid. The amount 
should never exceed 0.06 per cent. 



RUBBER MANUFACTURE 



Iron Sesquioxide 

There are several terms used for 
practically the same ingredient, the 
sesquioxide of iron. We see it sold as 
rouge, red ochre, Venetian reel, red 
hematite and under a few other 
names. In general use they are all 
inferior to the antimony colors, but 
they are useful iu the manufacture of 
non-poisonous articles and hard rub- 
ber, where it behaves better than the 
antimony. 

Rouge 

Rouge is made by calcining the sul- 
phate of iron and if this is done in 
the presence of barium or calcium 
sulphates, a more brilliant color is ob- 
tained. It has a specific gravitv of 
5.0 to 5.2. 

Red Ochre 

Red ochre is made by heating yel- 
low ochre, which is a clay containing 
siliceous matter along with a hydrated 
iron oxide. So the red ochre is really 
a rouge diluted with a siliceous mat- 
ter and is consequently of less value 
than the rouge. 

Red Hematite 

Red hemitate is the mineral fer- 
ric oxide and is of sufficient purity 
and of such a color that it is used as 
a red pigment in ebonite and articles 
that must be heat-resisting. 

Venetian red and indian red are 
artificial ferric oxide. 



Ve 



ilion 



Vermilion is a sulphide of mercury 
and is the most brilliant of all red 
pigments, likewise the most expensive, 
therefore, not used so extensively. It 
is employed in dental rubbers and 
must be free from all soluble mercury 
salts. 

It occurs in nature as the mineral 
cinnabar. It is produced artificially 
by heating the black sulphide in a 
covered cast-iron pot and the cinna- 
bar will be sublimed. This is often 
purified still further. 

It is adulterated with iron oxide, 
red lead aud sometimes gypsum. Its 
purity is easily tested by heating some 
in a porcelain dish. If no adulterant 
is present it will completely vola- 
tilize, leaving no residue. 



Black Pigments 

Under black pigments occur large- 
ly different grades of carbon, the com- 
monest being lampblack. 

Lampblack 

This is made by collecting the car- 
bon which results from the incom- 
plete combustion of oils, fats, resins, 
coal and like organic bodies. As a re- 
sult of the varied starting oiit ma- 
terials, we naturally get varying 
grades of lampblack. It generally 
contains some greasy materials and 
the amount of these present should be 
determined by an acetone extraction. 

Lampblack should not show more 
than 5 per cent of grease and should 
leave practically no ash. Lampblack 
has a specific gravity of 1.8 and has 
come into extensive use just recently. 

A short time ago it was used only 
in boots, shoes, carriage cloth, and 
druggist supplies but today it is one 
of the important ingredients used in 
a large number of mechanical goods 
and extensively in tire stock, where it 
appreciably increases the strength of 
the stock as well as its wearing sur- 
face. 

Bone Black 

Bone black is obtained by calcin- 
ing defatted bones in closed vessels 
out of contact with air. This grade of 
carbon, therefore, runs very high in 
mineral matter, very often equaling 
90 per cent of the whole. It is .coarse 
and harsh, even after grinding, and, 
although a black pigment, finds only- 
limited use. 

Gas Carbon 

Gas carbon is a pure grade of 
lampblack which is quite popular 
with certain manufacturers at pres- 
ent. 

Black Hypo 

Black hypo is a pigment which has 
been used in the past to some extent 
but is received with less favor at 
present. It is made by heating to- 
gether a mixture of litharge, sulphur 
and lampblack. The composition of 
the resulting product is uncertain. It 
contains some lead sulphide, a little 
free sulphur and some of the lead 
salts of oxygen sulphur acids. It 
has been made by adding sodium 
thiosulphate to a solution of sugar 



THE MANUFACTURE AND USE OF INORGANIC FILLERS 



of lead, when lead thiosulphate is pre- 
cipitated, and is sold as white hypo. 
If, however, this is heated, it changes 
to black, due to the formation of the 
sulphide. During the vulcanization 
process, if white hypo has been used, 
it will suffer the same change and pro- 
duce a black rubber. Its use at pres- 
ent is waning. 

Graphite 

Graphite is a form of carbon oc- 
curring in the free state in a high 
degree of purity and is also an arti- 
ficial product today. It is made in 
electrical furnaces, where coal is sub- 
jected to a very high temperature 
for a period of twenty-four hours. 

graphite is used in rubber goods 
more as a filler perhaps than as a 
pigment. Its coloring power is not 
very great. It will stiffen rubber ar- 
ticles and has remarkable lubricating 
properties, preventing the rubber 
from sticking to metals. It is used 
in the compounding of steam joint- 
ings and goods that are going to be 
subjected to a high temperature. 

Lead Sulphide 

Lead sulphide is also used as a black 
pigment, whether it is added as such 
or in the form of some other lead salt 
which changes into the sulphide dur- 
ing vulcanization. It is the most 
abundant form of lead found in 
nature as galena. 

Yellow Pigments 

Now we will mention some of the 
common yellow pigments. 
Yellow Ochre 

Just as we had a red ochre so there 
is a yellow ochre. The red variety 
is the pure ferric oxide, but if this 
is mixed with clay or siliceous mat- 
ter, it loses its red color and vary- 
ing shades of orange and yellow 
result. It is a natural occurring prod- 
uct and is inert in rubber. It is very 
cheap and the color it produces in 
rubber lacks brilliancy. 

Chrome Yelloiv 

Chrome yellow is the chromate of 
lead and is made by adding a solution 
of sodium chromate to a solution of 
lead acetate, when the yellow precipi- 
tate is produced. It finds extensive 



use in the manufacture of toys and 
cold cured goods, where its lead con- 
tent does not interfere. 

Cadmium Yellow 

Cadmium yellow, which is the sul- 
phide of the metal, is one of .the best 
yellow pigments. It is made by pass- 
ing hydrogen sulphide into a solu- 
tion of a soluble cadmium salt. It 
gives to rubber a fine yellow color 
and is not affected by vulcanization. 
It may be used in toys as it is non- 
poisonous. The cost of this material 
has practically eliminated its use. 

Arsenic Trisulphide 

Arsenic trisulphide is an excel- 
lent yellow pigment as it is not 
affected by vulcanization, but it is so 
extremely poisonous that its use has 
been almost abandoned. When it is 
mixed with a small amount of zinc 
oxide, it will produce a beautiful 
cream colored yellow. 

Yellow Dyestuffs Used 
The yellow colors are found large- 
ly, however, in toys, surgicals and 
tilings, and beside the pigments men- 
tioned above, to-day Ave find large 
quantities of organic dyestuffs being 
used instead of the mineral pigments. 

Green and Blue Pigments 

Green and blue pigments are used 
in the same line of goods as the yel- 
low ones, and they too are being re- 
placed by the organic dyestuffs. A 
few of each, however, are still im- 
portant enough to be mentioned. 

Chrome Green 

Chrome green is the sesquioxide of 
chromium. It is made by melting 
together one part of potassium 
dichromate and three parts of boric 
acid, then dissolving out the potas- 
sium boi*ate, when there will remain 
the beautiful green powder. It is 
inert in rubber and is not affected by 
vulcanization. 

Rinmann's Green 

Kallmann's green is made in al- 
most any shade of green desired. 
Chemically it is zinc cobalt oxide 
and by varying the two metals, dif- 
ferent shades are produced. It is 
made by calcining the precipitate 



RUBBER MANUFACTURE 



formed when a solution of sodium 
carbonate is added to a solution con- 
taining the sulphates of zinc and co- 
balt. It gives a fairly good green 
color in cold cured goods. 

Ultramarines 

On the border line between the 
green and blue pigments, we find the 
very interesting substance known as 
ultramarine, existing as a green pig- 
ment or a blue one depending on its 
method of preparation. 

No one knows to what it owes its 
color. It is made by heating to bright 
redness in a covered crucible for 
three or four hours an intimate mix- 
ture of 100 parts of pure kaolin, 100 
of dried sodium carbonate, 60 of sul- 
phur and 12 of charcoal. Chemically 
we should expect such a mixture to 
give the silicate of sodium, the alumi- 
nate of sodium, and sodium sulphide/ 
which might give the whole mixture a 
brown color, but on the contrary the 
mass is green and is known as ultra- 
marine green. It is a permanent 
color and is used as an inert pigment. 

If this green is powdered, washed 
with water and dried, then mixed 
with one-fifth of its weight of sul- 
phur and gently roasted until 
the sulphur is removed, and this re- 
peated again perhaps if necessary, 
the residue will possess a beautiful 
blue color and as such is known as 
ultramarine blue. This is used in 



the production of blue rubber 
articles, tiling, etc. 

Acids have the power of destroy- 
ing both the green and the blue color 
of these ultramarines. 

Prussian Blue 

Prussian blue is made by adding 
a solution of potassium ferrocyanide 
to a solution of a ferric salt. The 
blue pigment formed is filtered, 
washed and dried. This blue com- 
pound will produce a blue stock but 
not quite as good as ultramarine. It 
may be used when an acid resistant 
material is needed and ultramarine 
cannot be used. On the other hand, 
however, alkalis will decompose it. 
Prussian blue does not withstand 
the effect of vulcanization as well as 
ultramarine blue. 

Thenard's Blue 

Thenard's Blue is made by heating 
together in a covered crucible alumi- 
num and cobalt phosphates. The blue 
color which is obtained will depend 
upon the proportion of aluminum and 
cobalt used : the more cobalt employed 
the darker will be the shade of blue. 
This pigment is not used to any great 
extent. 

In these two chapters, which, on 
account of the material they contain 
appear very choppy, we have tried 
to give the reader a little insight into 
the commonest of ingredients used 
in the rubber industry. 



CHAPTER XIII 
The Manufacture and Use of Organic Accelerators 



In the minds of some people there 
seems to exist a misunderstanding in 
regard to the terms " accelerators " 
and " catalysts." Therefore it does 
not seem out of place here to point 
out^the true meaning and correct use 
of the two terms. 

Brezelius knew that hydrogen 
peroxide, if allowed to stand by itself, 
decomposed very slowly into water 
and oxygen. He also knew, however, 
that if to this hydrogen peroxide was 
added a small amount of finely 
divided platinum, a rapid decomposi- 
tion of the peroxide took place and a 
great volume of oxygen was liberated. 

He went further and found out 
that the platinum was not changed in 
itself in any way and that a small 
amount of platinum was capable of 
transforming an indefinite amount of 
hydrogen peroxide into water and 
oxygen. The two elements, hydro- 
gen and oxygen, will remain mixed 
together at ordinary temperature al- 
most indefinitely without any chemi- 
cal union, but if a little platinum 
sponge is introduced into the mix- 
ture, the union immediately takes 
place, yet the platinum remains un- 
changed. 

Sulphur dioxide does not combine 
with oxygen under ordinary condi- 
tions but in the presence of platinized 
asbestos, the two react and form the 
anhydride of sulphuric acid, thus the 
production of sulphuric acid today 
by the " Contact Process." 

By these three examples it will be 
seen that certain reactions are made 
to take place under certain condi- 
tions, by the addition of what might 
be regarded as a foreign substance. 
This foreign substance is necessary to 
change the speed of the reaction and 



is not changed in the least by it as 
far as we know. Such substances 
Brezelius called " catalysts." their 
action he called ' ' catalytic ' ' and the 
phenomenon " catalysis." Catalysts 
will not incite reactions to take place 
which would not take place at all but 
they do wonderfully affect the speed 
of these reactions. 

Action oj Catalysts 

It has been suggested that these 
catalysts, in effecting their work, 
form intermediate products which 
are very unstable and break down 
giving the products of the reaction 
and the renewed catalyst. Such in- 
termediate products have been proved 
to exist and to these has been given 
the name " pseudo-catalytic phe- 
nomena." Ostwald however pro- 
poses the idea that they act like a 
lubricating oil in a rotating wheel. 
It turns very slowly and with great 
difficulty when oil is lacking but 
when it is added, the wheel turns 
freely yet the oil has no part in the 
movement. Here will be seen the 
analogy to catalytic action. 

Euler has advanced the hypoth- 
esis that the velocity of a reaction de- 
pends upon the free ion concentration 
and that catalysts have the power of 
modifying this concentration, for we 
have, beside these catalysts which in- 
crease the speed of a reaction and 
are called " positive catalysts," 
those which retard a chemical change 
and are called " negative catalysts." 
Here we have set forth the true con- 
ception of catalizers, namely sub- 
stances which may hasten or retard 
a chemical change and yet are not 
themselves affected in any way. 

The term accelerators has quite a 
different meaning and application 



85 



86 



RUBBER MANUFACTURE 



from a chemical point of view. In 
the first place,' they only increase the 
velocity of the chemical changes and 
secondly they may or may not be 
affected chemically themselves. 

In the rubber industry, therefore, 
we should refer only to accelerators, 
for in the vast majority of cases, the 
substance which is added to increase 
the speed of vulcanization is in itself 
changed also. 



Only recently did it occur to the 
rubber chemists that it was possible 
to cut down the length of time of 
vulcanization, without inci'easing the 
steam pressure, by introducing into 
the rubber very small amounts of or- 
ganic substances which would act as 
accelerators. Once tried and the re- 
sults observed, the commercial im- 
portance of the practice was immedi- 
ately grasped. 

The introduction of these sub- 
stances was suggested from the fact 
that synthetic rubber, or caoutchouc 
was very difficult to vulcanize, as is 
also acetone extracted rubber. This 
led to the study of ways to vulcanize 
the synthetic product and to the 
study of the acetone extract from 
Para with the .result that nitrog- 
enous bodies were found in the ex- 
tract and the introduction of these 
into caoutchouc shortened its time of 
vulcanization. 

The work of research laboratories 
was directed toward the producing 
and perfecting of substances and 
learning also how they might be used. 
It is in the midst of this kind of work 
that we find ourselves today. In fact 
we do not know very much about this 
new line as yet and we must still be 
very modest in our claims. Many 
organic substances have been experi- 
mented with in this connection and 
new ones are being recommended and 
placed on the market every day. 
Some of them appear under their 
true chemical title while others are 
disguised under, trade names. Ke- 
cently this laboratory received one 
from a commercial house with the re- 
quest that some experimental work be 
done wi|h it and with the statement 
that they had not named it as yet. 



Several theories have been ad- 
vanced as to the part which these 
substances really play in hastening 
the cure of rubber 'articles, but we 
shall leave those to a future chapter. 

In this section we shall consider 
only a few accelerators and those are 
the ones - in commonest use. It is 
held today that only nitrogen com- 
pounds will act as accelerators, and 
only those capable of being easily 
handled, easily incorporated into the 
stock, and possessing great enough 
stability not to produce " blowing " 
during vulcanization, may be used. 
One of the first substances of this 
kind to be used was aniline. 

Aniline is made from nitro-benzene, 
which Js made from benzene. This is 
effected in large cast iron vessels 
where a mixture of nitric and sul- 
phuric acids is gradually poured into 
benzene. It is constantly stirred and 
the temperature maintained at 25 
deg. During the latter part of the 
reaction the temperature is raised to 
from 70 deg. to 90 deg. The mix- 
ture is then forced into a conical 
tank when the acid mixture settles to 
the bottom and is drawn off. The 
nitrobenzene is washed several times 
with water and then distilled in a cur- 
rent of steam. The equation for its 
production may be indicated thus. 
CH 





+H— 0— N— > 

II 





+ HOH 



The nitrobenzene is then placed in 
a cast iron cylinder provided with a 
stirrer, a reflex condenser and an 
opening for introducing iron filings. 
Some water is placed in the cylinder, 
some iron turnings and hydrochloric 
acid. These are kept stirred while 
nitrobenzene is added. The reaction 



THE MANUFACTURE AND USE OF ORGANIC ACCELERATORS 



87 



may be started by a jet of steam. 
Afterward, however, it will maintain 
its own temperature for operation, in 
fact one must guard against its get- 
ting too hot. At the end of the 
operation we have aniline, aniline 
hydrochloride, ferric oxide, some un- 
altered nitrobenzene and other im- 
purities. The main reaction which 
has taken place may be represented 
thus. 

CNO* 



6HC1 + 3Fe 




+ 2HOH + 3FeCl, 



But in actual working conditions it 
requires only about one-fourth of the 
theoretical amount of hydrochloric 
acid, thus showing that after a cer- 
tain concentration is reached, the re- 
duction is then effected by the action 
of iron on water in the presence of 
ferrous chloride in the following man- 
ner : 

CNO, 



+ 2Fe + 4HOH - 



+2Fe(OH) s 



After the reduction is complete, 
thick milk of lime is added until a 
distinct alkaline reaction is obtained 
when the mass is distilled with steam. 
The distillate will separate into two 
layers, the aniline being in the lower 
portion. This is often purified by 
redistillation. Aniline has a boiling 



point of 183 deg. to 184 deg. and a 
specific gravity of 1.024 at 16 deg. C. 
It is colorless when pure, but becomes 
brown in the air at a rate depending 
upon the amount of impurities 
present. 

This aniline oil has been used as an 
accelerator by simply pouring the oil 
into the compound when it has broken 
down on the hot mills. The vapors 
which came off from the mill were 
very injurious to the workmen, giving 
them aniline poisoning. The aniline 
acts upon the nervous system and 
even a small amount will turn the 
lips bluish and produce the effect of 
drunkenness, the patient becoming 
very pale and being affected with loss 
of appetite. The use of alcoholic 
liquors seems to be very harmful to 
one suffering from aniline poisoning. 

Factories in which aniline was be- 
ing used went to great expense to 
install ventilating systems with large 
hoods over the mills. It hastens the 
cure of rubber articles; makes vul- 
canization possible in a shorter time 
and also Avith the addition of less 
sulphur, which, of course, cuft. down 
the possibility of blooming. Aniline 
is a solvent for sulphur and that may 
have its influence upon shortening the 
time of cure as we know reactions 
take place more rapidly in solutions 
or homogeneous systems than in 
heterogeneous ones. 1'he use of ani- 
line alone has been practically aban- 
doned today in favor of those less 
harmful to the workmen and those 
existing in a form more easily han- 
dled. It serves, however, as a base 
for the production of some acceler- 
ators widely used at present. 

One of the first ones to be used and 
one that is still widely used is the 
product which is formed when aniline 
and carbon bisulphide are brought 
together. The principal product 
which is formed is diphenylthiourea 
or thiocarbanilide. The reaction which 
takes place may be expressed thus : 

S NHC C H 5 

|| NH„C f H, 

C + —■ y C = S + H 2 S 

II NH 2 C C H, | 

S NHC H S 

To produce this substance in the pure 



RUBBER MANUFACTURE 



form, Gatterman gives the following 
procedure : 

" A mixture of 40 grams of ani- 
line, 50 grams of earbon bisulphide, 
and 10 grams of finely pulverized 
potassium hydroxide is gently boiled 
for three hours in a water bath in a 
flask provided with a reflux con- 
denser. The excess of carbon bisul- 
phide and alcohol is then distilled off, 
the residue treated with water, the 
crystals separating out are filtered off 
and washed first with water, then 
with dilute hydrochloric acid, and 
finally with water. To obtain a high 
degree of purity, it is crystallized 
from alcohol." 

To produce the commercial prod- 
uct, all that is necessary is to place 
the mixture of aniline and carbon 
disulphide in large crocks or kettles 
in a warm place, where the escaping 
hydrogen sulphide will be carried 
away. The reaction will require per- 
haps thirty-six hours but it may be 
accelerated by the addition of sodium 
polysulphide. The yield is quantita- 
tive and there results a yellow, hard, 
crystalline mass. This is removed, 
pidverized, dried and is ready for use. 

It should have a melting point of 
154 deg. C. As an accelerator it is 
used in amounts from one-half to two 
per cent of the mixture. 

In using this material, great care 
should be taken to reduce it to a fine 
powder. In grinding it tends to flake 
up, making it rather difficult to ob- 
tain the fine powder. If it is not re- 
duced to a fine state of division, it 
will not be incorporated evenly in the 
rubber and will produce hard kernels 
of overcured rubber through the 
product. 

This substance shows its greatest 
effect in accelerating cure at the be- 
ginning of the process and thus great 
care must be used in milling it for if 
the rolls get too warm, vulcanization 
will begin. This same substance, 
thiocarbanilide, may be obtained in 
the market under the name of " Ex- 
cellerex." 

Tetramethylenediamine is an ac- 
celerator which gives fair results in 
the final product, yet is not to be re- 
garded, as rapid in its actions as some 
of the others. 



This substance is produced dur- 
ing the putrefaction of animal mat- 
ter and is called putrescene. In 
this connection we might call atten- 
tion to the results of Eaton and 
Grantham's experiments in the rapid 
curing of rubber. It will be remem- 
bered that they obtained a fast cur- 
ing rubber when they coagulated by 
means which would allow of the 
putrefaction of some nitrogenous 
matter, and the thought arises that 
this accelerating action may be due 
to the formation of tetramethylene- 
diamine. 

It may be produced on the com- 
mercial scale by first treating ethyl- 
alcohol with sulphuric acid, when the 
following reaction takes place : 
aH 5 OH + H = S0 4 — > CJS.SO.H + HOH 
with the formation of ethyl sulphuric 
acid. This substance then decom- 
poses and yields ethylene thus : 

CJB^SO^H > CJE 4 + BLSO, 

If the ethylene gas is then passed 
into bromine, the ethylene bromide 
is immediately formed. 

C=H, Br Br— C = H, 



C = H„ 



Br 



Br— C = H, 



Upon treating the ethylene bromide 
with potassium cyanide, the nitrile 
will be formed. 
Br KCN CN 

I I 

C = H., C = H, 

| + __». | -|-2KBr 

C = H, C = EL. 

| KCN | 

Br CN 

This nitrile upon reduction with 
sodium in a hot alcoholic solution 
yields the tetramethylenediamine. 
CN 



C = H, 



C = H„ 



+ 8H 



CN 
H 3 NCH 2 CH 2 CH 2 -CH 2 -NH J 

The substance is crystalline in nature 
and easily incorporated into the rub- 
ber. 

Another product related to the one 
above is hexamethylenetetramine. 



THE MANUFACTURE AND USE OF ORGANIC ACCELERATORS 



It is used in small quantities to di- 
sulphur musts and wines. Here it is 
called urotoropine. However, in this 
use it is in connection with sulphur 
as is also its use in the vulcanization 
of rubber. This substance is a deriva- 
tive of formaldehyde and results 
when formaldehyde is treated with 
ammonia. Its reaction is shown in 
the following : 
6HCOH+4NH, — > (CH 2 ) 6 N 4 +6HOH 

F. Hermann has given the follow- 
ing method for the production of this 
substance. To the formalin in a closed 
receptacle, he added ammonium chlo- 
ride in quantity sufficient to liberate 
enough ammonia to effect the above 
reaction with the amount of forma- 
lin flken, then enough caustic soda to 
free this ammonia from the ammo- 
nium salt. As rapidly as the am- 
monia is liberated, it will react with 
the formalin and produce hexa- 
methylenetetramine. This substance 
finds a wide use today as an accel- 
erator of vulcanization. 

Paraphenylenediamine also is an 
accelerator quite largely employed in 
the rubber industry today and yet 
it is a very poisonous substance. Great 
care should be taken where it is used 
to guard the welfare of the work- 
men. It is regarded as one of the 
rapid accelerators. It may be made 
in several ways. First by the reduc- 
tion of aminoazobenzene dissolved in 
aniline, with hydrogen sulphide or tin 
and hydrochloric acid. Second, by 
heating paradichlorobenzene or para- 
chloraniline with ammonia in the 
presence of a copper salt. (Ger. Pat. 
204408). 

Beginning with aniline in the first 
method, the following steps are neces- 
sary according to Holleman. 

Aniline treated with sodium nitrite 
in the presence of hydrochloric acid 
gives diazobenzenechloride, thus: 
C 6 H 5 NH 2 + NaN0 2 + 2HC1 — y 
C„H S N -NCI + 2HOH + NaCl 

When this is treated with aniline the 
diazoamrnobenzenechloride is pro- 
duced. 



One of the most characteristic re- 
actions of these diazoaminobenzenes 
is their easy conversion into isomers, 
or the aminoazo compounds. This is 
best carried out by adding aniline 
hydrochloride to a solution of diazo- 
aminobenzene in aniline and warming 
the mixture on a water bath. 

C H,N-NNHC H 5 — > 
C G H 5 N-NC H 4 NH 2 

Here the amino group is in the para- 
position to the azo group. When this 
compound is reduced there results 
aniline and paraphenylenediamine. 

C.H.N NC H 4 NH„ 

H 2 H 2 — *" 

NH 2 
C 



C..H-NH, 



CNH, 

The second method is very simple as 
indicated above. 





NH„ 



.CI h; 



CI H • NH 2 



C.H.N-N :C1 + H ■ NHC 8 H B 



Under the trade name of " Accele- 
rene," we find the substance para- 
nitrosodimethylaniline. It may be 
made by heating aniline hydro- 
chloride with methyl alcohol. 

NHHC1 



-4- 2CH 3 OH 



C 6 H 3 N ; N NHC e H s + HC1 



CH, 



N— CH S 



RUBBER MANUFACTURE 

H 



+ 2H0H + HC1 



The hydrogen in the para-position of 
these dialkylamines is readily re- 
placed by different groups. Thus the 
action of nitrous acid yields para- 
nitrosodimethylaniline. This sub- 
stance possesses a greenish color and 
should have a melting point of about 
85 deg. C. 

Piperidine and some of its deriva- 
tives have been used, but, owing to the 
poisonous nature of these substances 
and their odor, they are not used to 
any great extent. 

Piperidine is made by reducing 
pyridine with sodium and alcohol. 



NH 



CH„ 




N 



CH 2 

It is a liquid possessing an odor of 
pepper. It acts directly as an ac- 
celerator, however, upon vulcaniza- 
tion. 

Quinoline and its derivatives are 
used in a satisfactory manner to a 
limited extent. Quinoline being the 
base of these, we shall outline only 
methods for the production of that 
substance. It is found in coal-tar and 
bone oil but is difficult to obtain from 
these sources. 

Konigs first synthesized it by pass- 
ing allylaniline vapor over red hot 
lead oxide, when the following reac- 
tion took place. 





+ 2HOH 



Skraup's synthesis for quinoline as 
outlined by Perkin and Kipping is 
as follows : ' ' Concentrated sulphuric 
acid 100 parts is gradually added to 
a mixture of aniline, 38 parts, and 
nitrobenzene, 24 parts, and glycerine, 
120 parts, and the mixture is then 
very cautiously heated in a large 
flask (with reflux apparatus) on a 
sand bath ; after the very violent re- 
action which soon sets in has subsided, 
the liquid is kept boiling for about 
four hours. It is then cooled, diluted 
with water, and the unchanged nitro- 
benzene separated by distillation with 
steam; soda is then added in excess 
to liberate the quinoline and the un- 
changed aniline from their sulphates 
and the mixture is again steam dis- 
tilled. As these two bases cannot well 
be separated by fractional distilla- 
tion, the whole of the aqueous distil- 
late is acidified with sulphuric acid 
and sodium nitrite added until 
nitrous acid is present after shaking 
well. After heating, to convert the 
diazo salt into phenol, the solution is 
rendered alkaline with soda and again 
submitted to distillation with steam. 
The quinoline in the receiver is finally 
separated with the aid of a funnel 
and purified by fractional distilla- 
tion." It is a liquid with a peculiar 
odor. 



4- CHOH + > 




-4HOH 



This, being a liquid, is not easily 
handled so it is converted into its 
sulphate and used most frequently 



THE MANUFACTURE AND USE OF ORGANIC ACCELERATORS 



91 



thus. It is made by dissolving the 
quinoline in dilute sulphuric acid, 
when the sulphate (C 9 H 7 N) 2 H„S0 4 
crystallizes out. 

In addition to the ones mentioned 
above, many more have been tried ; in 
fact, derivatives of all possible nitro- 
gen compounds have been experi- 
mented with. Derivatives of the pro- 
teins of urea and ammonium com- 
pounds have all been recommended 
for this use. 

Aldehyde ammonia, which is pro- 
duced by passing dry ammonia gas 
into a solution of formalin, is a very 



good accelerator. It tends, however, 
to make the finished product harsh 
rather than of a velvety appearance. 

Many substances which will ac- 
celerate must be discarded, for accel- 
eration of cure alone is not a suf- 
ficient test for them. In addition to 
shortening the time for curing, they 
must also increase the physical prop- 
erties of the rubber and thus reduce 
the deterioration of the finished prod- 
ucts. So research along this line will 
continue even though at present we 
seem to be settling down to a few 
common accelerators. 



CHAPTER XIV 
The Manufacture and Use of Rubber Substitutes 



In this chapter, we shall consider 
those materials which are used in the 
rubber industry along with rubber 
compounding, and the ones we shall 
mention contain no rubber in them- 
selves, yet by their use, the actual 
amount of true rubber used may be 
reduced. The introduction of these 
materials must be done in such a way 
as not to be injurious to the final 
product, and likewise the substances 
themselves must not impair the phys- 
ical properties of the articles. 

The justification of the use of 
these materials in the beginning Avas 
especially to cut down the cost of 
the rubber goods by introducing 
some materials possessing properties 
like rubber yet which could be pro- 
duced at a much smaller cost. 

Such materials were found possible 
of production from many drying and 
even non-drying oils. It has been 
observed and known for many years 
that certain vegetable oils when ex- 
posed in a thin film to the air, or 
when in other words, were allowed to 
dry, formed a skin which possessed a 
few properties of rubber, such as 
toughtiiess and_ elasticity to a certain 
degree. What has really taken place 
is that the oil has been slowly taking 
up oxygen and has been converted 
into this semi-rubber like condition. 

As early as 1846, Sacc produced a 
rubber like material by actually oxi- 
dizing linseed oil rapidly by the use 
of nitric acid. If linseed oil is heated 
in contact with air until it has oxi- 
dized to the state of a semi-solid mass, 
then nitric acid is added and the 
heating continued, it will finally 
arrive at such a state that when 
cooled in the air, a solid material re- 
sults. This substance resembles rub- 
ber in "appearance, is more or less 



elastic, softens in hot water, and is 
soluble in turpentine, carbon d'sul- 
phide, and alkalies. When an alka- 
line solution of this product is 
treated with hydrochloric acid, it is 
precipitated unchanged. This prop- 
erty of oil of being changed by a 
process of oxidation in this manner 
is characteristic of drying oils in con- 
trast to non-drying oils, which upon 
exposure to the air become rancid. 
This oxidized oil is known as " Oil 
Rubber," and because it is of com- 
mercial importance a more rapid 
method for its production was nec- 
essary. By the process mentioned, 
above, the oxidation takes place only 
at the surface of the oil, or where it 
comes in contact with the oxygen of 
the air. 

To expose a greater surface of the 
oil to the oxidizing agent, a process 
has been patented whereby the hot, 
finely divided oil comes in contact 
with the air. This shortens the time 
of blowing the oil very materially. 
The final oxidation, however, is 
effected with nitric acid. The concen- 
trated nitric acid is diluted with twice 
its volume of water and this and the 
thick blown oil are boiled together. 
The oil becomes thicker and thicker, 
but boiling is continued until a sam- 
ple, when cold, will scarcely take the 
impress of a finger-nail. When this 
stage is reached, it is removed from 
the acid and is washed with boiling 
water until it is free from acid as 
determined by actual test. The oil 
rubber may now be formed into any 
desired shape and is ready for the 
market. It is used as an insulating 
material for electric wires. 

Because of this property of oils to 
form addition products with oxygen, 
and due to the chemical analogy 



92 



THE MANUFACTURE AND USE OF RUBBER SUBSTITUTES 



93 



which exists between oxygen and sul- 
phur, and the fact that sulphur is 
used in the vulcanization of rubber, 
it occurred to someone that it might 
be possible to cause the oils to form 
addition products with sulphur 
similar to those with oxygen. In 
other words it seemed possible to pro- 
duce a " vulcanized oil " with prop- 
erties more nearly like those of rub- 
ber than oil rubber possessed. 

Thus it was found that by heating 
certain oils with sulphur, there re- 
sulted a substance possessing some de- 
gree of elasticity. This method of 
heating an oil with sulphur produces 
a dark colored product and this is re- 
ferred to as " Brown or Black Substi- 
tute " or " Brown Factis." Its pro- 
duction resembles the " hot cure " 
process in the vulcanization of rubber 
itself. The oils most frequently used 
for this purpose are linseed, maize, 
cotton seed, and rape oil. 

Many formulas and methods of 
procedure to produce Brown Substi- 
tute have been given from time to 
' time, but we shall outline but three. 

First, from linseed oil. If this oil 
is heated to 100 deg. C. and then from 
5 to 10 per cent of sulphur is added 
and the temperature gradually 
raised to 130 deg. C, then allowed to 
cool back to 100 deg. C. and held 
at that temperature for some time, 
the vulcanizing will be complete. 
"When the reaction is finished, the 
product is cooled on a smooth cold 
surface. 

Second, if 8 gal. of corn oil are 
placed in a large boiler and rapidly 
brought to a temperature of 390 deg. 
F., during the heating a frothy curd 
will form over the surface of the oil 
which must be removed. During 
this heating, a current of hot air is 
blown through the oil which causes 
it to become more or less viscous. At 
this point, 0.20 lb. of sulphur, which 
has been previously melted, are 
added in the molten state. A vigor- 
ous reaction immediately begins and 
the whole mass froths up and is then 
poured into cooling boxes where it is 
stirred and allowed to cool. Black 
substitute then results. 

The sulphur used here must be 
free from sulphurous acid and this 



fact must be determined by analysis. 
This black substitute may be soft- 
ened by heat and cast into blocks and 
we find it in the industry largely in 
this form. 

Another process for making Brown 
substitute from corn oil has been pat- 
ented by William K. Leonard. This 
patent calls for 76 per cent of corn 
oil, 21 per cent of sulphur and 3 per 
cent of paraffin. The oil is placed in 
a kettle where it may be heated and 
when a temperature a little below 300 
deg. F. is reached, the sulphur and 
paraffin are added. The temperature 
is still raised and at about 310 deg. 
F. the reaction begins and the source 
of heat "is removed. The reaction 
will continue of its own accord, and in 
fact it being an exothermal reaction, 
the temperature will continue to rise 
often reaching 340 deg. F. during the 
process. The product is allowed to 
cool and is then ready to be incor- 
porated into rubber compounds. (U. 
S. Pat. 615, 863.) 

In 1846, Alexander Parkes mixed 
some linseed oil with from 20 to 40 
per cent of sulphur monochloride 
and found that vulcanization would 
take place and a light-colored product 
result, what we call today " "White 
Substitute " or " White Factis." 
This process is analogous to the " cold 
cure " which is used with rubber. 
It was found out later that if the 
oil was first dissolved in carbontetra- 
chloride the reaction would take 
place in a great deal better manner, 
thus more nearly resembling the cold 
cure vulcanization. 

Only small quantities of oil are 
treated at a time as the exothermal 
reaction causes such a rise in tem- 
perature that there results a big loss 
of the sulphur monochloride and the 
oil itself will carbonize. The mono- 
chloride used must be free from the 
dichloride of sulphur. This is very 
objectionable as it causes too violent 
a reaction with the result that the 
oil carbonizes and tin? product is 
burnt. 

The amount of sulphur taken up by 
.the oil varies from 5 to 15 per cent. 
The amount, however, will depend 
upon the degree of oxidation of the oil 
before the monochloride is added, that 



RUBBER MANUFACTURE 



is. partially oxidized oils, or blown 
oils, will not take up as much sul- 
phur. This same fact is true in re- 
gard to the making of Brown Factis. 
and that is the reason that the oils are 
first heated. 

Henriques found that raw linseed 
oil requires at least thirty parts of 
sulphur monoehloride to solidify 

when fresh while it requires only 
fifteen to eighteen parts when :: 
been heated for some hours at 200 deg. 
C. in contact with the air. He also 
observed that if the temperature is 
raised from 250 deg. to 300 deg.. then 
10 per cent of sulphur monoehloride 
will suffice. All drying oils seem to 
behave in this same manner. 

The same oils which are used for 
the production of Brown Factis may 
be employed for the production of 
the White. The raw oil is placed in 
shallow pans, which arc constructed 
in such a way that air may be blown 
up through the heated oil in them. 
The oil is first heated to a tempera- 
ture of 392 deg. F. to 464 deg. F. and 
the white scum which forms is re- 
moved : then air is blown up through 
the oil and the temperature raised to 
572 deg. F. This partially oxidized 
oil is now run into large storing tanks 
or reservoirs where it is allowed to 
cool to ordinary temperature. The 
reason for this treatment, as was 
pointed out above, is to save sulphur 
monoehloride. less of which is re- 
quired with these oxidized oils. 

A weighed quantity of this cold 
thick oil is placed in a large enam- 
eled boiler and stirring is begun. 
When the required amount of sul- 
phur monoehloride is added, white 
vapors will soon appear, indicating 
that the reaction has begun and their 
cessation will serve as an indication 
of the completion of the reaction. 
The mixture of oil and monoehloride 
is maintained at a temperature of 
131 to 140 deg. F. The factis is re- 
moved and placed upon nets, which 
allow the escape of the odor of the 
sulphur monoehloride. The product 
is almost colorless and is not affected 
by boiling with dilute acids and alka- 
lies ia 7 distinction from the brown 
factis which is soluble in alkalies. 



William K. Leonard has also pat- 
ented a process for the production 
of the white substitute. According 
to his patent, 64 per cent of corn 
oil and 13 per cent of castor oil are 
thoroughly mixed and then 21 per 
cent of the entire mass of sulphur 
monoehloride. 0.5 per cent of naph- 
tha and 1.5 per cent of oxide of 
magnesia are added. The reaction 
immediately begins and the tempera- 
ture tends to rise, but when the re- 
action is completed and the whole 
mass allowed to cool, a white sponjrv 
produet will result. I U. S. Pat. 615,- 
864.] 

For the production of a white 
factis from linseed oil, Nieolaus Beif 
has patented a form of apparatus 
for mixing the oil and sulphur mono- 
chloride under pressure in such a 
manner that the whole mass is mixed 
by a rotary movement and expressed 
from the apparatus by a similar 
movement thus reducing the mixture 
ro a flake-like condition? TJ. S. Pat. 
1.006.274/ 

Henriques has prepared a table 
showing the production of "White 
Factis from different oils : 
Linseed oil congeals with SO p:u-r< sulphur 

monoehloride, but not with 25 parts. 
Poppy oil conceals with 35 parrs sulphur 

monoehloride, but not with 30 parts. 
Rape oil congeals with 2a parts sulphur 

monoehloride, bur not with 20 parts. 

m seed oil congeals with 43 parrs sul- 
phur monoehloride. but not with 40 

parts. 
Olive oil conceals with 2a parts sulphur 

monoehloride. but not with 20 parts. 
Castor oil conceals with 20 parts sulphur 

monoehloride. but not with IS parrs. 

It is really remarkable to what ex- 
tent factis may be used in rubber 
without affecting the elastic proper- 
ties of the rubber, in fact it may be 
added up to a proportion of 1:1. 
This is due to the mechanical con- 
sistency of factis. which posse-- s 
comprcssile elasticity, but is desti- 
tute of tensile strength. So by its 
addition we may sacrifice tensile 
strength, but not impair springi- 
ness. 

The specific gravity of factis varies 
between 0.95 and 1.02 and it is the 
only material by which floating goods 
may be cheapened. 



THE MANUFACTURE AND USE OF RUBBER SUBSTITUTES 



95 



Brown Faetis often contains paraf- 
fin wax or heavy petroleum frac- 
tions, both of which are added to 
the oil before it is vulcanized. Gen- 
erally we are safe in saying that the 
less there is of unvuleanized oil in 
a substitute the better it is. for the 
free oils have a tendency to shorten 
the life of the goods. The best White 
Faetises are those which are driest 
and least coherent in the ground 
state and the combined per cents of 
sulphur and chlorine should not ex- 
ceed twenty. 

H..C — — CO — CH„- 



influenee upon the amount of sulphur 

to be added. 

The exact chemistry of the pro- 
duction of these substitutes is not 
known, yet the possible steps may be 
indicated. 

We do know that the oils which 
are used are glycerides of the fatty 
acids: therefore we may draw the 
following picture where two mole- 
cules of one of these glycerides are 
bound together by three molecules of 
sulphur monoehloride S„CL. 

When this White Faetis is treated 
with a boiling alcoholic solution of 
CH — CH — (CH S )„ — CH,, 



CI 



S 



CI s 

IlC — — CO — CIL — CH — CH — i CH,) 13 — CH, 

I 
H..C — — CO — C1I, — CH — CH — (CH.),« — CH, 

I I 

CI s 

I 

CI s 

I I 

H..C — — CO — CH, — CH — CH — (CH„) 18 — CH, 

"I 
HC — — CO — CH. — CH — CH — (CH.,) v . — CH, 

I ! I 

Cl s 

I I 

I Cl s 

I II 

H„C — — CO — CH, — CH — CH — (CH„) l3 — CH, 



The free sulphur content must be 

known whenever a faetis is used in 

compounding for this will have its 

x-CH- CH- 



N/2 potassium hydroxide, it is 
saponified and the sulphur atoms 
will remain bound to the fatty acids. 



S 
I 

S 
CH- 



y 
ci 

ci 
i 

CH-y 



+ 2K0H ■ 



C = CH — y 

I 
S 

I 

s 

I 

C = CH — y 



+ 2KC1 + 2H0H 



RUBBER MANUFACTURE 



The Brown Factis may then be 
represented in the following manner : 



substance is insoluble in all known 
solvents. 



I-LC — — CO — CH, — CH — CH — (CH,) 13 — CH 3 
I I 

s s 

I I 

HC — — CO — CH, — CH — CH — (CH 2 ) 18 — CH, 

I 
H„C — — CO — CH, — CH _ CH — (CH.) i- — OH, 

I I 

s s 

I I 

H 2 C — — CO — CH 2 — CH — CH — (CH,) 13 — CH 3 

HC — — CO — CH, — CH — CH — (CH„) r , — CH, 
I "I' 

s s 

I I I 

H 2 C — — CO — CH, — CH — CH — (CH,) 13 — CH, 



From these formulas it will be 
seen why a partially oxidized oil 
will require less sulphur or sulphur 
monochloride for the oxygen will go 
into the substance in the place of 
these. 

The substances which have been 
treated above are substitutes only 
in the sense that by their use, the 
actual amount of rubber taken may 
be reduced, but we may mention a 
few substances which have been 
made that are substitutes for rubber 
itself. In other words, they may be 
made up into articles in which rub- 
ber has been used before. Such a 
substance is Sulphuretted Hydro- 
cellulose. It was discovered by 
Sthamer and is made by treating 
finely ground hydrocellulose with 
enough hydrochloric acid of 24 deg. 
Baume at ordinary temperature to 
form a thin paste of the nature of a 
solution. To this sulphur mono- 
chloride is added and the whole mass 
stirred. After some time the fluid 
turns turbid and when placed in 
cold water, the sulphuretted hydro- 
cellulose settles to the bottom in one 
large mass. It is removed and 
placed upon a screen where it is al- 
lowed to drain and the excess acid 
thus recovered, then washed with 
water until free from the acid. This 



When tins material is compounded 
with rubber and then subjected to 
vulcanization, it will decompose and 
give up its sulphur to the rubber 
which in turn is cured. It seems that 
such a substance might find more ap- 
plication in the rubber industry. 

Several patents have been taken 
out by Julius Stoekhausen for the 
making of a substitute for india rub- 
ber. In one of these, 125 grams of 
gelatin are dissolved in 125 grams 
of glycerine and this then mixed 
with 5 to 20 grams of sulphur, 20 
grams of camphor, and 15 to 20 
grams of colophony. This mixture 
is heated for a long time and there 
is added to it 10 to 20 grams of for- 
maldehyde or 3 to 10 grams of 
sodium bichromate. This produces 
an elastic and plastic substance. 

He has also patented the follow- 
ing formula: 125 grams of powdered 
gelatin or agar-agar are dissolved in 
125 grams of crude glycerine, 25 
deg. Baume at 70 deg. C. Then 15 
grams of tar and 25 grams of naph- 
thalene are added and finally 20 
grams of 4 per cent formaldehyde are 
used for hardening. This substance 
may then be cast into molds of any 
desired shape. 

We might go on and enumerate 
many, many such substances which 



THE MANUFACTURE AND USE OF RUBBER SUBSTITUTES 



have appeared from time to time, 
but it hardly seems advisable. 

Within the last few years, the 
practice of adding the bitumens and 
pitches has become very common. 
The Trinidad and Syrian asphaltum 
has been used for some time in the 
insulating of cables, but now these 
and bitumen in the form of mineral 
rubber are being used in compounds 
even as high as 50 per cent of the 
rubber content. These mineral rub- 
bers are many in number and are 
made from soft natural bitumens or 
from blown petroleum residues. In 
the trade, we find the substances 
M.R.X. and Rubrax as examples of 
these materials. The real value of 
any of these must be determined by 
actual use and their properties de- 
termined by mixing and vulcanizing. 
A great deal has been said and writ- 
ten of late in regard to the different 
effects produced by high and low 



softening point products. We do not 
wish to enter into that controversy 
here, but it has been claimed that 
high softening point mineral rubber 
produces a high tensile rubber but 
one with low resiliency, while low 
softening point material produces a 
low tensile but good resiliency. Thus 
we have an excuse for the manufac- 
ture of both grades. 

Some resins of natural occur- 
rence are used as rubber substitutes 
and we simply wish to mention 
rosin, shellac, copal, acroides, san- 
darac, dammar which are regarded 
as resins proper. Then, we find 
growing in the tropical regions 
plants which produce a resin con- 
taining also a certain percent of rub- 
ber itself. These substances appear 
under the names of Jelutong, Palem- 
bang, Pontianak and Dead Borneo. 
These materials all find a limited use 
in the rubber industry. 



CHAPTER XV 
Theories of Vulcanization 



The term vulcanization is derived 
from " Vulcan," the Roman fire god, 
its connection with regard to rubber 
being therefore the heat which causes 
rubber when mixed with sulphur, to 
assume entirely different physical 
and chemical properties. 

There are two general methods of 
vulcanization, namely, what is known 
as the " cold cure " and the " hot 
cure vulcanization." The former is 
effected by the use of a sulphur mono-- 
chloride solution, which acts upon the 
rubber, and as it is a surface action, 
it may be employed only with very 
thin articles. This method is also 
allowed to take place by placing the 
articles to be vulcanized in the vapors 
of sulphur monochloride. 

The credit for this process belongs 
to Parkes, who, in 1S46, dipped thin 
strips of caoutchouc, for different 
lengths of time, in to a solution of 100 
parts of carbon disulphide and 2.5 
parts of sulphur monochloride. After 
dipping these strips, he quickly dried 
them at 78 deg. F. and then washed 
them in warm water. The process 
has been modified somewhat since his 
day but the essential features were 
known to him. 

The credit for the " hot vulcaniza- 
tion " should be divided between 
Hancock and Goodyear, who inde- 
pendently discovered that rubber, 
when heated in contact with sul- 
phur, changes its properties very ma- 
terially. 

Thej' arrived at this conclusion, 
however, by slightly different means. 
Hancock in 1843 patented a process 
for vulcanization whereby he sub- 
jected sheets of rubber to the action 
of molten sulphur heated to a tem- 
perature of 284 deg. to 302 deg. F., 
when the rubber took up 10 to 15 



per cent of sulphur. Of course, these 
sheets had a great tendency to bloom, 
so he washed them with a solution of 
soda. At the same time Hancock 
was trying these experiments, Good- 
year was working along the same 
lines, only he was mixing the sulphur 
into the rubber, until he had a homo- 
geneous mixture which he subjected 
to a high temperature. Of course, the 
two results were similar, but Good- 
year's method being, in many ways, 
the easiest to control, is the one which 
has survived. Gerard found that it 
was possible to effect vulcanization by 
subjecting the rubber for three hours, 
under a pressure of four atmospheres 
in a solution of calcium pentasulphide, 
to a temperature of 265 deg. F. The 
articles are then removed and washed 
with warm water. They are well 
cured and will possess a velvety 
appearance. The length of time they 
must remain in such a bath, of course, 
is determined by the thickness of the 
articles to be vulcanized. 

Victor Henri in 1909-10, first ex- 
posed rubber to the action of ultra- 
violet rays and found that it under- 
went a kind of oxidation. Later it 
was found that, if a solution of rub- 
ber containing sulphur was subjected 
to the ultra-violet rays, the whole mass 
became thick and of a gelatinous 
nature, and by test showed combined 
sulphur. These vulcanized solutions 
may be used for rubberized cloth, 
used as cements, for rubberizing 
leather, or used in repair work of all 
kinds. 

The French have called this proc- 
ess " Cuisson " and the Germans 
" burning " but today " vulcaniza- 
tion " seems to be the accepted term. 

Inasmuch as the hot vulcanization 
process is dependent upon the tem- 



98 



THEORIES OF VULCANIZATION 



99 




RUBBER MANUFACTURE 



perature to which the rubber is sub- 
jected, as will be pointed out later, it 
is very essential that, during vulcani- 
zation, a close watch is kept of the 
temperature. A few years ago, al- 
though it was known that it was the 
temperature which effected the 
change, yet because the heat was de- 
rived from steam, which was meas- 
ured in pounds per square inch, 
steam pressure was the method of 
control used in vulcanizing rubber. 
This led to many very bad results. 
For instance, in a vulcanizer, you 
might have the desired pressure of 45 
pounds indicated by your pressure 
gage and yet there might be pocketed 
air at some place in the heater which 
is not at the desired temperature and 
faulty goods would result. 

There is no excuse for such trouble 
today when it is possible to obtain 
automatic, self-recording thermom- 



CH 3 ■ C • CH, • CH= • CH 

II " II 

CHCH.-CH-C-CH, 



+ 2S— *- 



eters like those put out by the C. J. 
Tagliabue Co. or those of the Bristol 
Co. 

What really takes place during vul- 
canization, or in other words, the 
chemistry of what causes this marked 
change in the properties of the rub- 
ber, was not investigated to any great 
extent until 1902 to 1910. Up to this 

CH, 



ories of vulcanization which later 
came in for their amount of criti- 
cism. We shall here bring forth the 
main points which he developed. 

Previous to this time the impres- 
sion had existed that when rub- 
ber was mixed with sulphur and then 
heated, substitution took place. 
Weber showed conclusively that this 
was incorrect for he pointed out that 
if this were true, an immense volume 
of hydrogen sulphide must be pro- 
duced, which is contrary to our work- 
ing experience. Thus the substitu- 
tion theory was abandoned and in its 
stead, Weber recommended the addi- 
tion theory. According to that the- 
ory if we accept the formula for 
caoutchouc as recommended by Har- 
ries, we have a compound with double 
bonds at which points addition is 
possible. 
CH • C ■ CH. • CH, ■ CH 
/ \ 

S | | s 

\ / 

CH-CH 2 -CH : -C-CH 3 

This will stand for rubber com- 
pletely saturated or hard rubber 
which has a constant per cent of sul- 
phur of approximately 32. This 
same reaction takes place in the cold 
cure, only Hinrichsen has pointed out 
that the reaction undoubtedly takes 
place between two such molecules 
thus: 

CH 



C — CH, CH, CH S - 

II " II + 1 
CH • CH, CH, C CI 


- S CH ■ CH, ■ CH, C 

1 + II II 
CI C— CH„CH„CH 


1 
CH, 

CH 3 


1 
CH 3 

CH 3 


C — CH, CH, CH — S - 


-S — CHCH.CH.- C 



CH — CH,- CH, C — CI CI— C — CH, CH, ■ CH 

I I 

CH, CH 3 



time, the process had been regarded 
as purely a chemical phenomenon. 

Weber's Theory 

The early work of a scientific 
nature along this line was conducted 
by Weber and he laid down the- 



Weber pointed out that the amount 
of sulphur which actually entered 
into vulcanization was dependent to 
some extent on many factors, most 
important of these, however, being 
the amount of sulphur really present 
and capable of entering into the re- 
action, and second the temperature at 



THEORIES OF VULCANIZATION 



which the vulcanization was taking 
place, and third the length of time it 
was subjected to this temperature. 
By varying these conditions, we ob- 
tain different degrees of vulcaniza- 
tion ranging from a soft consistency 
up to hard rubber for ebonite. 

In order to have some scale for 
comparing this degree of vulcaniza- 
tion, Weber suggested the term " co- 
efficient of vulcanization." That is, 
in all grades of cured rubber, we have 
sulphur in at least three modifications. 
There is " total sulphur," " free sul- 
phur ' ' and ' ' combined sulphur, ' ' the 
latter being the amount of sulphur 
which is in combination with caout- 
chouc. It is the ratio of this sulphur 
to the total amount of rubber present 
in the finished product which is called 
- the coefficient of vulcanization. 

The unfortunate thing about the 
use of this is the fact that the 
same coefficient of vulcanization with 
different grades of rubber produces 
entirely different results, and, in 
fact, different results in the same 
rubber if it is handled in different 
ways. "Weber came to the conclu- 
sion that this range of vulcanization 
from soft rubber to ebonite could be 
represented by the formation of ten 
sulphur compounds with caoutchouc, 
the lowest having a formula of 
(C 10 H 1( .) 10 S, and the highest ex- 
pressed by the formula C, H 16 S,. 
As proof of this he found that when 
determining the combined sulphur 
in samples cured for different lengths 
of time with an excess of sulphur 
present and then plotting the com- 
bined sulphur with its per cent 
on one axis and time expressed on 
the other, he obtained a broken curve 
which he took as evidence of a chem- 
ical change taking place. These are 
the points adduced by Weber in 
support of his theory. We shall now 
give a brief review of the theory of 
W. Oswald concerning vulcanization. 

Oswald's Theory 

W. Oswald was of the opinion that 
vulcanization might be explained bet- 
ter upon the grounds of the physico- 
chemical theory of absorption deal- 
ing with colloids than upon Weber's 
purely chemical theory. 

This theory of Oswald's is found 



in Z. Chem. Ind. Kolloide, 1910, 6, 
136-155, as it may be applied to vul- 
canization, and he points out the fol- 
lowing facts in support of his theory : 

First — Regardless of the amount 
of sulphur added to rubber, whether 
large or small, there always remains 
after vulcanization a certain amount 
of it in the free state, while the chem- 
ical theory would require that if 
small in amount, it should all be 
combined. 

Second — If vulcanized rubber is 
extracted with petroleum spirit, sul- 
phur will continue to be removed as 
long as any remains in the rubber 
and this same, is true of unvulcanized 
rubber only the sulphur is extracted 
more rapidly. 

Third — The adsorption of sulphur 
by rubber is always additive. 

Fourth — A continuous series of ad- 
ditive products is formed and yet 
the amount of sulphur in the series 
does not conform to the law of mul- 
tiple proportions. 

Fifth — The amount of adsorbed 
sulphur will depend upon the previ- 
ous mechanical working of the rub- 
ber. The more the mechanical work- 
ing, the greater the amount of sur- 
face produced and thus the greater 
the adsorptive power of the rubber. 

Sixth — The adsorption increases 
with rise of temperature and con- 
forms more nearly to what should be 
expected from a physico-chemical ad- 
sorption than from a chemical change 
alone. 

Seventh — The adsorption of sul- 
phur is not regular as the sulphur 
curve shows changes in direction. 

Eighth — The adsorbtion of sul- 
phur proceeds more nearly according 
to the adsorbtion formula than to any 
chemical one. That is, 

^=kc"' 
a 

Where x = amt. of adsorbed sub- 
stance, 

a = amt. of adsorbent. 

c = initial concentration of 
substance which is ad- 
sorbed. 

k and m are constants. 

From these facts, Oswald concludes 



RUBBER MANUFACTURE 



that vulcanization is to be consid- 
ered as an adsorption of the sulphur 
by the rubber. Hinrichsen and E. 
Kindscher studied the reaction which 
takes place during cold vulcanization 
(Z. Chem. Ind. Kolloids, 1910, 4). 
They prepared a solution of rubber 
in benzine, using a known quantity 
of rubber. To this they- added 
a known quantity of sulphur mono- 
chloride dissolved in benzine and al- 
lowed the two to react for three 
weeks. At the end of this time, they 
determined the amount of unchanged 
sulphur monochloride and by dif- 
ference they ascertained the amount 
which had reacted with the known 
amount of rubber. They came 
to the conclusion that for a certain 
amount of rubber, the amount of ad- 
sorbed monochloride is constant and 
is independent of the amount taken. 
They then calculated a formula for 
this final compound which they wrote' 
as indicated above (C 10 H 10 )„ S 2 Cl 2 . 
This work seems to favor, therefore, 
the idea of a chemical change during 
vulcanization but Oswald pointed out 
that this simply represented the 
maximum amount of adsorbed sul- 
phur and represented that part of 
the sulphur curve which was parallel 
to the axis. 

These same men later carried out 
the following test with hot vul- 
canization. They prepared a solu- 
tion of rubber in cumene of such a 
concentration that each 100 c.c. of 
the solution contained two grams of 
rubber. To several such amounts 
they added 1, 2, 3, 4, 5, 6, 7 and 8 
grams of sulphur respectively. The 
mixtures were then all subjected to a 
temperature of 170 deg. C, while 
being agitated by carbon dioxide. In 
each case, the product which resulted 
did not contain more than 32 per 
cent of sulphur and therefore agreed 
with "Weber's formula of C 10 H 16 S„ 
showing that here perhaps is a chem- 
ical compound capable, therefore, of 
being represented by a formula. 

Following the appearance of Os- 
wald's theory we find a great deal of 
investigation and discussion along 
this line. 

Spence's Experiment 

Spence"' and his workers in this 



country did a great deal of work on 
this theory of vulcanization. For in- 
stance, they studied the velocity with 
which free sulphur is extracted from 
vulcanized rubber by use of hot ace- 
tone and came to the conclusion that 
the last portions of free sulphur are 
removed very slowly but that a point 
is reached where no more sulphur 
may be removed. Therefore, in con- 
tradiction to Oswald's theory, they 
claimed that a definite amount of sul- 
phur had really entered into chem- 
ical union with the rubber during 
vulcanisation. They do, however, 
agree with Oswald in that they be- 
lieve that the free sulphur may be ad- 
sorbed. 

Reversability of Vulcanization Process 

P. Bary and L. Weydert (Comptes 
Rend., 1911, 153, 676-679) did apiece 
of work to prove that the process 
which takes place during vulcaniza- 
tion was one which might be reversed. 
They extracted some vulcanized rub- 
ber with hot acetone until all free sul- 
phur was removed and then heated 
the extracted rubber for eight hours 
at 145 deg. C. in carbon dioxide. Fol- 
lowing this they extracted again with 
hot acetone and repeated the previous 
treatment twice more with the result 
that the final amount of combined 
sulphur was less than in the orig- 
inal sample. Therefore, they felt 
that they had reversed the process 
of vulcanization to a certain extent. 
This is a very important point in the 
controversy for if vulcanization may 
be reversed, it lends great weight to 
the adsorption theory, while, on the 
other hand, if it is impossible to re- 
verse the process, then it argues in 
favor of Weber's theory. They were 
also of the opinion that during vul- 
canization, the rubber itself was de- 
polymerized. 

Migration of Sulphur in Rubber 

H. Skellon has carried out some 
experiments dealing with the migra- 
tion of sulphur in rubber during vul- 
canization. He superimposed two 
sheets of rubber containing different 
percentages of sulphur and then sub- 
jected them to vulcanization condi- 
tions and came to the following con- 
elusions : 



THEORIES OF VULCANIZATION 



103 



That migration takes place either 
upward or downward with equal 
facility. 

That equilibrium is very quickly 
arrived at in the two sheets during 
vulcanization, and then the concen- 
tration of the free sulphur in the rub- 
ber is the same in the two sheets. 

That the evidence points to the 
fact that vulcanization is most prob- 
ably 

(1) Melting of the sulphur; 

(2) Solution of the sulphur in 
rubber ; 

(3) Slow combination of the sul- 
phur with the rubber. 

Skellon made a study of the effect 
of the polyprene sulphide during vul- 
canization and came to the follow- 
ing conclusions: 

Let us picture vulcanization to be 
represented by the following reaction 

(C 10 H 10 )„ + NS 2 <— >NC 10 H 1B S S 
If this is true, we should expect that 
during vulcanization, the ratio of 
rubber to sulphur remains the same 
and therefore the reaction should pro- 
ceed at the same rate of speed, but by 
actual experiment, this is found not 
to be the case. The speed of vulcani- 
zation is decreased as the process goes 
on. This is explained by Skellon to 
be due to the fact that sulphur is 
more soluble in polyprene sulphide 
than in rubber and therefore the law 
of partition comes in and we actually 
have some of the sulphur extracted 
from the rubber by the sulphide 
which is formed, hence more sulphur 
will be dissolved by it and the last 
stages of the cure will proceed very 
slowly as a result of this. 

Researches by Loewen 

II. Loewen has carried out a very 
interesting experiment favoring the 
idea that the process of vulcanization 
consists in the sulphur's first dissolv- 
ing in the rubber and then combining 
chemically with it, in contrast to the 
adsorption theory of Oswald. 

To study this phenomenon, he 
placed a small amount of rubber with 
10 per cent of its weight of sulphur 
on a microscope slide and placed 
over it a cover glass. This slide he 
then subjected to a temperature of 



130 deg to 140 deg. C, and at regu- 
lar intervals made microscopic exami- 
nations of it. 

At first the sulphur melted and the 
globules could be seen through the 
rubber itself, later the globules dis- 
tributed themselves throughout the 
whole mass and by continued heating, 
the whole mass became clear or trans- 
parent, but he observed further that 
as this cooled, it became cloudy due 
to the separating out of the globules 
of rubber which, as we know, change 
back in cooling to the rhombic form. 
Then, again, if the slide is heated 
until upon cooling it still remains 
clear, then when the excess sulphur 
does separate it will do so in the 
crystalline form and not appear as 
globules first thus resembling solu- 
tions. He also found that sulphur is 
more soluble the higher the degree of 
vulcanization and calls attention to 
the fact that hard rubber does not 
tend to bloom even though it may 
have a large per cent of free sulphur. 
This is explained, therefore, on the 
ground that the sulphur, being more 
soluble, here remains in solution. He 
then placed some rubber alone on a 
slide and placed over it the cover 
glass and around the edges of the rub- 
ber he placed molten sulphur. After 
regular intervals of heating, he would 
examine it with the microscope and 
found that the sulphur diffused into 
the rubber to some distance as would 
be expected during solution of one 
in the other. 

These experiments led Loewen to 
the firm belief that vulcanization was 
truly a chemical process. (Gummi- 
Zeit. 1913, 27, 1301-1302.) 

Vulcanization and Viscosity 

Dr. Gustave Bernstein in a report 
before the Rubber Congress, held in 
London, 1914, showed how he had 
studied vulcanization from the stand- 
point of viscosity. He is of the opin- 
ion that rubber must be depolymer- 
ized before it can enter into chemical 
change, that is, it must change phys- 
ically from (C 10 H 16 )„ to NC 10 H lfl . 
All of the agents which will depol- 
merize rubber will also reduce its vis- 
cosity. He also observed that the vis- 
cosity of all completely depolymer- 
ized rubber was the same. He also 



RUBBER MANUFACTURE 



called attention to the fact that all 
the physical agents that bring about 
■depolymerization, cause a vulcaniza- 
tion action to take place when the 
rubber is mixed with sulphur. An 
example of this is seen when a so- 
lution of rubber and sulphur is ex- 
posed to the ultra-violet rays. Its 
viscosity immediately increases. If 
this is true, then our vulcanization is 
to be explained upon the ground that 
the heat first depolymerizes the rub- 
her and then the sulphur repoly- 
merizes it. 

In support of this theory, he points 
out the fact that while mixing sul- 
phur and rubber on the rolls at a 
temperature not exceeding 80 deg. C, 
vulcanization took place and by an- 
alysis, 0.8 per cent of combined sul- 
phur was found, while upon heating 
the same mixture in an oven at 80 
•deg. C for the same length of time 
no combined sulphur was found. 

The conclusion to be drawn is that 
the mechanical work assisted the de- 
polymerization of the rubber and the 
sulphur then entered into combina- 
tion. Then if this be true, the sul- 
phur must act partly at least in the 
capacity of a catalytic agent. That 
this is true follows from the work of 
Helbronner where he found that 
actinic light had really vulcanized 
the solution of rubber and sulphur 
and yet the amount of combined sul- 
phur was only 0.6 per cent. This 
fact is still borne out by the addition 
■of a small amount of sulphur to aid 
in the polymerization of isoprene to 
produce synthetic rubber by the 
Badische Anilin process. The rub- 
ber obtained by this process is poly- 
merized more highly than the nat- 
ural rubber. 

He therefore draws the following 
conclusions: first, that what we call 
vulcanization is a repolymerization : 
-second, smaller quantities of sulphur 
than are ordinarily used are capable 
of effecting this change ; third, the 
amount of combined sulphur is not 
Tieeessarilv a measure of the degree 



of vulcanization as claimed by C. 0. 
Weber. 

The following idea has also been 
brought forward. As we know cer- 
tain physical agencies have the power 
of lowering the viscosity of rubber 
and this points to its depolymeriza- 
tion. However, the action of physical 
agencies, like ultra-violet rays, upon 
sulphur in solution is to polymerize it 
and thus make it into an insoluble 
colloidal form. Therefore, vulcaniza- 
tion is first depolymerization of the 
rubber and at the same time polymeri- 
zation of the sulphur and then we 
ma j 7 think of the depolymerized rub- 
ber as adsorbing the colloidal sulphur. 

Upon this theory we might explain 
the deterioration of rubber under the 
influence of certain physical agencies 
as due to the continuation of the de- 
polymerization of the rubber and the 
increased polymerization of the sul- 
phur. 

Ostromislensky's Theory 

I. I. Ostromislensky has recently 
advanced what may be looked upon 
as a combination theory made up of 
the two others. He suggested that 
vulcanization consisted first in a 
small amount of sulphur forming a 
derivative with the caoutchouc which 
may be regarded as the vulcanizing 
substance, second this substance is 
then adsorbed by the remaining rub- 
ber and the whole mass is regarded as 
vulcanized. Thus it will be seen that 
it is first a chemical change and then 
an adsorptive process. It is in this 
state of reasoning and theorizing that 
we find ourselves today. 

From work carried out in this 
laboratory, we have come to the be- 
lief of Spenee that it is a chemical 
change and that when accurate de- 
terminations of the combined sulphur 
are made on samples taken at short 
intervals of time, the sulphur curve 
will become a smooth one without the 
kinks in it which Weber found, and 
may thus be looked upon as a true 
chemical change. 



CHAPTER XVI 
Methods of Reclaiming Rubber 



In this section, we shall consider 
the different ways in which rubber 
which has been once used may be 
treated and thus returned to com- 
pounds. 
•This of course includes a great 
many different processes because of 
the great variety of compounds or 
stocks which furnish the material to 
be reclaimed and then too the great 
number of stocks into which the 
shoddy may be worked. 

We shall have therefore as raw ma- 
terial which is to be reclaimed, first, 
unvulcanized stock in the form of 
trimmings. This may have in it fab- 
ric, mineral fillers and its free sul- 
phur. Second, the vulcanized stock, 
ranging in degree of vulcanization 
from soft cure up to hard cure or 
ebonite. These materials may contain 
fabric, fillers, and even metal as we 
find the metal beads in tires, free 
sulphur and substitutes. Third, we 
have hard rubber waste itself. 

The first class of material very sel- 
dom comes into the hands of the re- 
claimer proper for being unvulcan- 
ized. All that is necessary is to treat 
the waste with a rubber solvent like 
naphtha. A great deal of the waste 
does not contain even fabric, but 

CH, — C — CH, CH„ — C — II 

VI )\ 

S I IS 

vl 1/ 

CH— CTL, CH, — C — CH 3 

simply the rubber plus the sulphur 
and mineral fillers, and when the 
solution is effected, the naphtha solu- 
tion is wrung out of the fabric if it 
is present, and if absent it is decanted 
from the mineral matter. The solvent 



is then evaporated and the rubber is 
thus reclaimed. This is a very simple 
process, and, although strictly speak- 
ing it is a form of reclaiming, yet it 
is one that is not regarded as such 
in the reclaiming industry. 

The big problem that confronts the 
reclaimer is the handling of the sec- 
ond class of materials, namely that 
which has been vulcanized and thus 
had some of its chemical and physical 
properties changed by some of the 
sulphur having entered into chemical 
union with the caoutchouc. 

Therefore every man when he ap- 
proaches the problem does so with 
the idea that he will be able to find 
a process whereby the original hydro- 
carbon will be found again in a form 
capable of the same degree of vul- 
canization that it possessed before it 
ever went into a rubber compound. 
In fact he tries to split off the sul- 
phur atoms in the vulcanized mole- 
cule and thus go back to the un- 
saturated hydrocarbon. 

This might be represented as the 
reverse of the action which took place 
during vulcanization and might be 
called devulcanization. 

This would represent the process 
in the case of ebonite. That this 



CH, 



c — 


CH„ 


• CH 2 — CH 


1! 

CH- 


-CH, 


1! 

II +2S 

II 

• CH„ — C — CH, 



goal has never been reached and that 
it is not probable that it will be 
reached seems apparent today. 

The formula C 10 H 10 S, as we have 
mentioned before represents hard 
rubber, yet the rubber which has been 



105 



106 



RUBBER MANUFACTURE 



subjected to reclaiming contains much 
less combined sulphur than this 
formula indicates. 

The above formula contains ap- 
proximately 32 per cent of sulphur, 
while the material used by the re- 
claimer will average about 3 per 
cent or even less. It would appear 
therefore that a large part of the rub- 
ber is not vulcanized and that all that 
would be necessary to obtain the un- 
vulcanized rubber would be to treat 
the product with a suitable solvent, 
then evaporate it off and the rubber 
would thus be obtained. But this is 
not the case, for the combined sul- 
phur and the product in which it 
exists are very securely bounded and 
held together. 

However, to effect the above men- 
tioned change many patents have 
from, time to time appeared, many .of 
which have never been put into prac- 
tice and many of which have been 
allowed to lapse. We shall simply 
mention some of these and when 
doing so will classify them as to 
whether they are purely mechanical 
processes or chemical ones. The latter 
may be either ' ' Acid " or " Alkali. ' ' 

Devulcanization Processes 

In 1857, Conrad Poppenhusen and 
Ludwig Held suspended finely di- 
vided rubber in different solvents and 
then conducted into this mixture dry 
ammoniacal gas. The gas is absorbed 
and the gum swells, the whole mass 
becomes viscid, and this material is 
then suitable to be used in new com- 
pounds. 

One of the oldest methods was pre- 
sented by Hiram L. Hall in 1858. 
In this process the vulcanized rubber 
was boiled up with water in a caldron 
after it had been reduced to a finely 
divided state to make it semi-plastic. 
It could then be put into compounds 
again. 

In 1860, Edward Simon patented 
a process in which he subjected one 
hundred parts of shredded waste 
vulcanized India rubber and two 
parts of chloride of lime to an open 
heat at a temperature of 1000 deg. to 
1100 deg. F. The rubber melted and 
during*' constant stirring the sulphur 
was distilled out. The plastic mass 



which remained could then be worked 
into new stocks. 

In 1861, John Murphy took out a 
patent for the reclaiming of rubber 
whereby the old rubber was mixed 
with sulphur and vulcanized until it 
formed hard stock. This was then 
formed hard stock. This was reduced 
to a powder and then mixed with 
unvulcanized gum and made into 
whatever form was desired and this 
vulcanized. This was a peculiar man- 
ner, to say the least, of using waste 
rubber. 

In the same year, Charles Mc- 
Burney patented the idea that by 
mixing old vulcanized rubber which 
• had been reduced to a fine state with 
oils like pine or rosin oil, cottonseed 
oil, olive oil, castor oil, palm oil, or 
cocoanut oil, and allowing it to stand 
for several hours, then by adding raw 
rubber and the necessary fillers for 
which the product is intended, the 
material may be all incorporated on 
a mill and vulcanized. It thus af- 
fords a way of using old rubber. 

Thomas J. Mayall in 1862 proposed 
that vulcanized rubber waste might 
be rendered fit for use again by grind- 
ing the material to a fine powder. He 
then made up a batch composed of 
five-eighths of this old rubber and 
three-eighths of a vegetable oil or 
pine ojls and mixed them thoroughly 
on a mill. This material was then 
subjected to a gentle heat. 

In 1863, Alfred Ford patented in 
England a process in which the old 
rubber is boiled with a strong solu- 
tion of alkali; the material is then 
powdered and placed in moulds which 
are subjected to a hydraulic pressure 
and heat of ordinary vulcanization by 
which the whole will be agglutinated. 

In 1863, Charles H. Hayward pat- 
ented what may be regarded as the 
acid process of today. 

In 1871, H. Smyser brought out a 
patent for the using of old rubber by 
simply reducing it to a fine powder 
on a grindstone and then incorporat- 
ing this dust into a new compound. 

In 1881, N. C. Mitchell defended 
by patent what are known as the acid 
processes. 

He reduced the rubber to be 



METHODS OF RECLAIMING RUBBER 



treated to a fine state of division, then 
placed it in a tight steam box in 
which a steam pressure of from 50 
to 75 lb. could be maintained. Into 
this box containing the rubber he 
placed sulphuric acid or muriatic 
acid of varying strength, depending 
upon the grade of compound to be 
treated. Then the whole was closed 
and the steam turned on for from 
one to five hours. The rubber was 
then removed, washed and dried. 
This treatment of course removes 
fabric from the compound as well as 
mineral fillers which are used. 

McDermott in 1882 modified the 
Mitchell acid process a little by add- 
ing alone with the charge of acid and 
rubber some manganese dioxide and 
a solution of potassium bichromate. 
Then he subjected the whole to steam 
under pressure, the result being prac- 
tically the same. 

In 1883, A. W. Kent patented an 
apparatus for the washing of ground 
rubber on a sieve, thus allowing the 
dirt and sand to be washed away, 
also the fiber, and allowing simply the 
vulcanized rubber with its fillers to 
remain. This is dried and as such is 
mixed with new compounds. 

In 1883, John L. Chadwick pat- 
ented a process for removing both 
cotton and wool fabric from vul- 
canized rubber. The scrap is first 
immersed in muriatic acid of 10 deg. 
Baume and then heated to from 200 
deg. to 212 deg. F. This continues 
for a couple of hours, when the cotton 
is destroyed. The material is then 
wrung out of the acid and passed 
through a wool picker. Not all of 
the wool is removed in this way, so 
it is then placed in a 22 deg. Baume 
solution of caustic soda. Before this 
all the aeid must be removed by wash- 
ing. "When removed from the soda 
solution and washed, it is in a good 
workable form. 

In 1884, J. J. Montgomery, sub- 
jected vulcanized rubber to the action 
of hydrocarbons obtained from pe- 
troleum, that have boiling points 
around 400 deg. to 450 deg. P., at 
a temperature of 350 deg. F. The 
rubber becomes a doughy or plastic 
mass from which the oils are removed 
by heat. 



In 1890, N. C. Mitchell patented 
a new modification in which the rub- 
ber after it had been ground and 
washed is heated with steam in the 
presence of calcium sulphide to which 
has been added some heavy petroleum 
which keeps the rubber in a moist 
condition. 

Maximilien Gerber in 1894 pro- 
tected his process of reclaiming by 
a patent whereby the rubber scrap is 
heated in a double bottomed closed 
vessel with a solvent for the gum 
along with a metal, in the finely di- 
vided condition, which has a great 
affinity for sulphur. Such metals are 
iron, tin, lead, zinc, mercury, etc., and 
the solvent being benzine, carbon 
tetrachloride and the like. 

The charge is heated to from 139 
deg. to 144 deg. C. for about eight 
hours; then it is allowed to stand in 
a receiver for twenty-four hours, 
when the sulphides and fillers will 
have settled out and the rubber solu- 
tion is decanted. The rubber is ob- 
tained by evaporating the solvent or 
as a solution is used to waterproof 
cloth. 

i In 1899, A. H. Marks patented 
/ what is known as the alkali process. 
By this method the ground rubber 
waste is brought to a temperature of 
344 deg. to 370 deg. F. in a 3 per 
cent solution of caustic soda. This 
is effected in a closed tank, and after 
a period of about twenty hours the 
process is completed, when the rubber 
is removed, washed and dried. This 
removes the free sulphur, the fabric 
and many of the fillers like lead com- 
pounds and aluminum ones. In 1900, 
he modified his patent by substituting 
a rotating cylinder which allowed a 
better mixing during the treatment 
with steam. 

In 1900, Johan Theilgaard re- 
claimed waste rubber with the use of 
potassium cyanide, but this is too 
dangerous a process to be recom- 
mended. 

In 1900, Robert Cowan patented 
a machine for removing foreign mat- 
ter from old rubber. Before this 
time, materials like nails, leather, 
strings and bark had been removed 
largely by washing. His machine is 
what is known as a strainer. The 



RUBBER MANUFACTURE 



rubber is fed into a machine which, 
by means of double walls, is heated by 
live steam to a temperature where the 
rubber begins to soften and then by 
a worm is forced through the strainer 
discs which retain the solid particles 
but allow the passage of the rubber. 
This machine in some modified form 
is used today in the reclaiming busi- 
ness in connection with the different 
processes for removing the iron. 
Along with it, however, a powerful 
magnet is also used to remove iron 
particles. In 1904, L. T. Petersen 
modified the alkali process by first 
treating the washed and shredded 
rubber with the alkali raised only to 
its boiling point. After the fiber is re- 
moved, the rubber is taken from this 
solution and treated with an aqueous 
solution of a hydrocarbon or oxy- 
hydrocarbon such as phenol under 
high temperature and pressure. The 
remaining alkali is here combined and 
the rubber reclaimed or rendered 
workable. 

In 1908, George Capelle reclaimed 
by using as a solvent the hydrocar- 
bons which result from the distilling 
of India rubber in vacuo. 

In 1909, Auguste Tixier treated 
rubber waste with terpeneol, which 
dissolved the rubber, and then he 
precipitated it by the addition of al- 
cohol. . 

In 1910, G. S. Heller patented 
what is termed the Electric Reclaim- 
ing Process. The rubber is first re- 
duced to a fine state of division and 
is then charged into a large metal 
cylinder which may be stationary and 
contain agitating paddles on the in- 
side, or it may be a rotating drum 
thus agitating the solution. Around 
the container is placed a large band 
which connects with one of the poles 
of a generator, and into the center of 
the drum projects the opposite pole 
from the generator. The following 
charge is placed in the retainer: 
100 lbs. of ground rubber, 600 lbs. of 
water, 21 lbs. of sodium hydroxide and 
1 lb. of ferric sulphate. The retainer 
is closed, steam is turned on and the 
contents heated to from 330 deg. to 
370 deg. F., the whole agitated and 
the electric current will also flow 
through this electrolyte, thus its 



name. The process requires from ten 
to twenty-four hours. The rubber is 
removed, washed, and dried. In 
many respects the product resembles 
that obtained by the alkali process. 

David A. Cutler in 1913 recom- 
mended the use of zinc chloride as 
a solvent for the fabric in the place 
of either acid or alkali. As a work- 
able charge he used : 35 lb. of ground 
rubber; S7.5 lb. of water; 17.5 oz. 
of zinc chloride; 4 lb. 6 oz. of oil, 
which is a distillate from pine wood. 
This is all thoroughly mixed in a tank 
and finally heated in a closed vul- 
canizer at a pressure of 100 lbs. of 
steam. The rubber is removed and 
washed. 

In 1913, H. W. Kugler modified the 
alkali process by adding to the charge 
two to five per cent of aniline. The 
charge is subjected to a pressure of 
from 60 to 150 lbs. of steam for eight 
hours. The rubber is removed, 
washed and dried. 

In 1915, Orrin A. Wheeler patented 
the following process: "The im- 
proved method of treating rubber 
scrap containing fiber is as follows : 
The scrap, such as tires, shoes, hose, 
etc., is ground and pulverized in the 
usual manner. The pulverized mate- 
rial is then treated with a strong solu- 
tion (about 20 per cent) of caustic 
soda and allowed to stand in a cool 
place approximately from three to 
five hours. Next the material is 
placed in a digester which is equipped 
so that it can be sealed or closed up 
tightly, and carbon disulfide (CS.,), 
about one pound more or less accord- 
ing to the character of the material 
treated to about ten pounds of diy 
rubber scrap, is added to the material, 
and then the digester is closed and 
hermetically sealed. This mixture is 
permitted to remain in the digester 
for from one to five hours to permit 
chemical reaction to occur, the di- 
gester being operated during such a 
period to stir and agitate the mass 
to facilitate the said reaction and 
thereby bring about a combination of 
the sulphur with the cellulose, and 
so producing a cellulose Xanthoge- 
nate. On completion of this reaction, 
the rubber and fiber are converted 
into a sticky cohesive mass. Next 



METHODS OF RECLAIMING RUBBER 



water in quantity approximately 
equal to the original dry rubber is 
added to the material in the digester 
and the agitation is continued, the 
water mixing with the cellulose to 
distend it. Next the mass in the di- 
gester is heated by carefully raising 
the steam pressure in the heating 
chamber around the digester to ap- 
proximately 100 lbs., which pressure 
is kept up for a period ranging ap- 
proximately from fifteen to twenty 
hours, according to the stock under 
treatment, and during such time 
agitation and stirring of the mass will 
be continued a part of or all the time. 
This heating causes the cellulose to 
bqcome insoluble in water and devul- 
canizes the rubber in the presence of 
caustic soda and carbon disulfide. In 
this process carbon disulfide tends to 
dissolve the combined sulphur and 
dissolves all the free sulphur, and 
when heated produces a high pressure 
in the digester, thereby causing thor- 
ough impregnation of every particle 
of rubber under treatment and great- 
ly assisting in the recovery of . the 
rubber. The solvent may, of course, 
be recovered. 

In this method of reclaiming rub- 
ber, the cotton fiber that is usually 
destroyed or removed in other proc- 
esses is permitted to remain with the 
rubber and utilized and becomes a 
valuable ingredient in both soft and 
hard rubber compounds. The rubber 
and elastic tenacious cellulose unite 
and intermingle so that an article 
made therefrom will possess the 
toughness and wearing qualities of 
new and pure rubber and will be su- 
perior for some purposes, particu- 
larly where the article made from the 
reclaimed product is to be subjected 
to heat, is exposed to the elements or 
to the action of oils, acids and al- 
kalis. Since the cellulose of the 
fibrous material in the scrap is 
utilized to advantage in the product, 
the cost is less than under any pre- 
vious process in which the fiber is 
destroyed and removed or removed 
without being destroyed. 

An excellent grade of material can 
be made from the product of the 
process with the addition of sulphur, 
and with the addition of some of the 



cheaper gums, such as pontianiac, 
acra flake, guayule, an article of a 
higher grade can be produced at a 
low cost. If desired new rubber may 
be added. 

A comparatively good grade of re- 
claimed rubber can be obtained by 
introducing the alkali and carbon 
disulfide at the same time, but better 
results are believed to result from the 
successive treatment with the alkali 
and carbon disulfide as herein before 
set forth. 

The invention is not to be under- 
stood to be restricted to the precise 
process and proportions set forth, 
since these may be modified by those 
skilled in the art without departing 
from the spirit and scope of the in- 
vention. 

In 1916, Gray Staunton ground 
rubber and cleaned it of fiber by a 
mechanical process. This material is 
then mixed in the proportion of 80 
per cent waste rubber and 20 per 
cent dry potassium carbonate. The 
mixture is placed on trays and placed 
in a tight heater and steam admitted 
to a pressure of from 15 to 60 lbs. 
The sulphur is removed as K 2 S S which 
is soluble in water. 

Rubber waste may be worked up 
with linseed' oil while heating and the 
resulting semi-liquid mass treated 
with sulphur monochloride when a 
so-called rubber substitute is pro- 
duced. 

In the above we have not men- 
tioned all of the various methods that 
have been suggested from time to 
time, in fact very few of the patents 
have been mentioned, but we have 
striven to give types. When a careful 
survey is made of all of these and 
the many other patents also, it will 
be perfectly apparent to all that 
there are only about two methods, 
namely, the alkali and acid processes, 
or perhaps a combination of these 
two into one called the acid-alkali 
method. 

Practically all patents claim to be 
able to remove all of the sulphur from 
the rubber, and yet the fact remains 
that no sulphur-free shoddy is to be 
obtained on the market. Therefore, 
there is a limit to the number of times 



RUBBER MANUFACTURE 



that the same rubber may be put 
through the reclaimer, and that limit 
is reached in ebonite or hard rubber. 
Today hard rubber is generally re- 
duced to a powder and incorporated 
into compounds simply as an inor- 
ganic filler might be. In the mind of 
the writer the most important thing 
in the reclaiming business, regardless 
of the method, is the removing of the 
fabric and free sulphur at as low a 
temperature as possible. We know 
that alkalis have a pronounced ac- 
celerating action upon the rate of 
cure of rubber ; therefore, when waste 
rubber containing free sulphur is 
placed in a devulcanizer of whatever 
type, and the alkaline solution added, 
and the steam turned on until a 
pressure of 60 lbs. or more is reached, 
there is every reason to believe that 
some additional vulcanization is sure 
to take place although we are carry- 
ing on what we term devulcaniza- 
tion. 

Then again it is imperative that 
as much as possible of the alkali be 
removed from the finished product 
either by washing or by the addition 
of a little acid to neutralize it, for 
if any remains it exists there as an 



uncontrollable accelerator in what- 
ever compound this shoddy may be 
used. 

By the acid process, the finished 
product seems to oxidize or deterio- 
rate more rapidly. It becomes hard 
on the surface and will easily crack. 

It might be worth while to try and 
see what kind of a product couid be 
obtained if the free sulphur was first 
removed from the ground rubber 
waste by extraction with hot ace- 
tone and then the application of the 
alkali method. That would prevent 
any further vulcanization during the 
reclaiming process. 

This question comes as a side issue 
to that of reclaiming. Is it possible 
to recover the cellulose in a form or 
modification from the acid or alkaline 
solution, depending upon the process 
used? Great volumes of cellulose are 
consumed here. Or could the soluble 
mineral fillers be profitably recovered 
from these solutions? These ques- 
tions may be answered some day of 
course, and make it possible to manu- 
facture valuable by-products from 
materials that are lost in the methods 
now used in reclaiming old rubber. 



CHAPTER XVII 
Preparation of Crude Rubber for Manufacturing 



The many processes through which 
crude rubber must pass before it is 
turned out into manufactured articles 
introduce many possibilities of its 
being ruined, or if not ruined, at least 
badly injured. 

Recall for a moment the steps 
which we have already mentioned, 
through which this material has 
passed ; also the different persons who 
have been directly responsible for its 
real value. Is it not to be marveled 
at that we get as good results as we 
do? The development of plan- 
tations under the supervision of 
trained men has greatly improved 
the treatment of the rubber in the 
earlier stages of its manufacture. But 



even today the native of Africa ob- 
tains and prepares his rubber from 
the vines of that country under very 
crude conditions; the South Ameri- 
can produces better rubber ; while the 
plantation rubber is best of all. The 
manufacturer of today obtains his 
rubber supply from all sources, rang- 
ing from that produced by the primi- 
tive method of the barbarian tinc- 
tured with the tricks of fraudulency 
and deceit which so called civilization 
has taught him, up to that produced 
by the more or less scientific method 
for producing uniform crude rubber. 
In this chapter we shall follow the 
rubber after it arrives at the fac- 
tory and we see it in the receiving 
room, on through the processes of 




Fig. 33 — Up-Rivek Fine Paea in Factory Stoeage 
111 



112 



RUBBER MANUFACTURE 



cleansing, drying, milling, calender- 
ing, and then leave it ready to be 
made up into whatever article its par- 
ticular compound has been designed 
for. 

The Receiving Room 

In the receiving room, we find the 
many varieties of rubber coming 
from many different sources, from 
many different species of plants, pre- 
pared in many different ways, put 
up in many different forms and dif- 
ferently stored. All these sorts must 
be put through the general proc- 
ess and each finds its own proper 
place in the finished article to which 
it is best adapted. We shall see there- 
fore all the different shipments each 
carrying its own number which num- 
ber identifies the life history of that 
particular lot. We will find that each 
lot is kept separate until it has en- 
tered into some compound. 

At certain times it may become nec- 
essary, after receiving large ship- 
ments of rubber, to store it for some 
length of time. This depends a great 
deal upon the market conditions and 
also the supply available. When the 
price is very low, there is a tendency 
toward large buying which means 
that it will be stored upon arrival. 



During certain seasons of the year in 
normal times, we find more rubber 
stored than in certain others. But 
whether stored or taken from the re- 
ceiving room directly, the first gen- 
eral treatment is the same, namely 
that of cleansing or washing. The 
grade of rubber determines how and 
to what extent this process must be 
carried out. The time was when all 
rubber brought into the factory was 
washed, but today the greater part 
of the plantation rubber is not 
washed, that having already been sat- 
isfactorily done on the plantation it- 
self. A very small portion of the 
plantation rubber is washed today in 
the factory, and only when it is used 
for certain special articles where the 
highest degree of cleanliness is re- 
quired. 

Washing 

The crude rubbers when taken into 
the wash room are treated, according 
to the form in which they come, in 
different ways. For instance, if the 
individual pieces are large, they must 
be cut into smaller ones. The rubber 
is then soaked in large tanks, which 
contain warm water, until it is soft- 
ened. From these tanks, the rubber 
is taken to a machine known as a 




Fig. 34 — Soaking Tank 



PREPARATION OF CRUDE RUBBER FOR MANUFACTURING 



113 



' ' cracker. ' ' This consists of two cor- 
rugated rolls turning toward each 
other at different rates of speed. 
Over these there is allowed to flow 
warm or cold water as is desired, 
while the rubber is passed between 
the rolls. Here the rubber is first 
torn into small pieces by means of a 
more or less grinding action, and for 
that reason it comes through in a form 
which is not adherent. In fact it may 
often be returned through the mill 
by the use of a shovel. Some kinds 
of rubber will remain adherent in the 
form of a thick heavy crepe. Fine 
Para is of this variety. 

In the next step we find a varying 
practice. In some factories, this rub- 
ber, after passing a few times through 
the cracker, is passed to the adjoining 
machine called a " washer." It is 
like a cracker in design but the cor- 
rugations of the rolls are much 
smaller, and the variation in speed 
of the rolls may not be as great. 
Here the rubber is washed and as- 
sumes a thick crepe form. Prom here 
it is given to the third and last ma- 
chine of similar design with practi- 
cally smooth rolls, which finishes the 
washing and leaves it in a thin sheet 
form. 

In some factories the rubber goes 
through the cracker and is then fin- 



ished on but one additional machine. 
That, however, requires the constant 
changing of the distance between the 
rolls, and introduces, therefore, the 
possibility of a variation in thickness 
in the finished sheets. 

Some forms of rubber, after going 
through the "cracker," are washed 
in beating machines. These are large 
oval shaped tanks with a partition 
running part way through the middle 
and parallel to their long axis. This 
partition allows the passage of the 
charge of the tank past both of its 
ends. On one side of the tank is 
placed a rotating cylinder over an ele- 
vation in the floor of the tank. When 
the rubber is placed in this machine 
and the cylinder rotated, the whole 
mass will circulate and pass between 
this drum and the floor thus pro- 
ducing a scrubbing action upon the 
rubber. This form of washing is 
used with rubbers which do not ad- 
here well into sheet form. 

Special washers have been designed 
for washing gutta percha and balata. 
These are washed in hot water in 
which they become soft. The ma- 
chines used are automatic to the ex- 
tent that after the material is added 
and the machines closed, a kneading 
process under hot water takes place, 
and the sand, bark and leaves are re- 




Fig. 35 — Washing and Sheeting Rubber 



114 



RUBBER MANUFACTURE 



moved. When the resins are re- 
moved from this washer they are 
sheeted in a smooth surfaced mill. 
The length of time consumed in 
washing should be as short as pos- 
sible. The mechanical working of 
rubber either on a washer or mill 
tends to depolymerize it and thus re- 
duces its nerve. 

Drying 

The next step is the drying of the 
rubber. This is effected in several dif- 
ferent ways. In the early days of the 
industry, the sheets of rubber were 
hung in large rooms which were kept 
rather warm and the rubber gradually 
■dried out. This required perhaps thirty 
days. The drying room capacity then 
had to be very large ; in fact the mini- 
mum would be thirty times the space 
used each day if it required thirty 
days to dry out. This process was 
slow and it required a large amount 
of space. To hasten this process, 
therefore, two principles recom- 
mended themselves. First, the chang- 
ing of the air in the drying rooms. As 
the air becomes saturated with mois- 
ture, evaporation takes place very 
slowly, so by forced ventilation the 
length of time of drying the rubber 
was reduced, and therefore the capac- 
ity of the drying rooms was in- 
creased. Then maintaining these 
rooms at a uniformly moderate 



temperature aided materially in the 
drying process. Where this method 
is used the rubber is hung over racks. 
The actual time required to dry the 
rubber depends also on the thickness 
of the sheets. As mentioned, it is a 
big advantage to have the sheets of 
uniform thickness so that they will all 
be dried at the same time; this is 
attained by having the washers 
set so that the last one through which 
the rubber passes need not be 
changed. Some forms of rubber are 
very soft and in a warm room will so 
soften that they will not support their 
own weight when hanging from the 
racks. To overcome this difficulty a 
different practice is resorted to. 

This consists in removing the water 
more rapidly from the rubber by plac- 
ing it in a tight chamber heated with 
steam coils from which the air may be 
removed. In other words, the rub- 
ber is dried in a partial vacuum. The 
rubber is placed upon trays which 
slip into these vacuum driers. Hejpe^ 
the rubber is dried in about three 
hours. This method has received con- 
siderable criticism upon the ground 
that it impairs the nerveTof the rub- 
ber, and some have contended that it 
could be used only with certain grades 
of rubber. But today more rubber is 
vacuum dried than ever before, indi- 
cating that the practice is here to 
stay. 




Fig. 36 — Stock Drying Room 



PREPARATION OF CRUDE RUBBER FOR MANUFACTURING 



115 



Another process of drying which 
has been used in cases of emergency 
is drying upon the hot rolls of mills. 
For instance, if the drying capacity 
of a factory is inadequate to supply 
the required amount of dry rubber 
to the compound room, the partially 
dried sheets are removed from the 
drying racks and taken into the mill 
room. Here they are placed upon 
large hot rolls, the moisture in the 
rubber is converted into vapor and as 
such is removed from the rubber. 
Being an emergency measure, this is 
resorted to very seldom. 

When the rubber hangs in drying 
rooms, it has been found best to have 
the rooms darkened as the light seems 
•not only to discolor the rubber but 
also to break it down or depolymerize 
it. 

Prom the drying process, the rub- 
ber goes to the compound room un- 
less it has been vacuum dried and in 
that case, it is generally stored for a 
short time. 

Mixing Mills 

We shall not discuss the process 
of compounding here as that will be 
dealt with in a future chapter, so we 
next find the rubber weighed out in 



batches with different fillers ready for 
the process of milling, or incorpor- 
ating the fillers into the rubber uni- 
fornily. This is done upon mills of 
varying sizes. The rolls are smooth, 
and rotate at different rates of speed. 
Through the axes of these rolls hot 
and cold water may be circulated 
either to warm or to cool them as the 
working of the rubber causes the rolls 
to become very hot. 

The rubber in the batch is first 
put upon the mill and worked until it 
is " broken down " or in other words 
becomes soft and flows evenly over the 
roll and between the two rolls. When 
this stage is reached, which is easily 
observed by the operator, the fillers 
are gradually added to the rubber 
and are incorporated into the rub- 
ber by returning it through the mill 
over and over again. 

Several things must be observed in 
milling. As mentioned in connection 
with washing, the mechanical work- 
ing of the rubber tends to depoly- 
merize it, and especially is this true 
where the temperature is above nor- 
mal. So upon the mill this effect is 
very marked. Therefore it is de- 
sirable to mill the rubber as rapidly 




Fig. 37 — Vacuum Dryer 



RUBBER MANUFACTURE 



as possible and yet it must be worked 
long enough to make it an even or 
homogeneous mass. The roll of the 
mill next to the operator is kept a 
little warmer than the other and ro- 
tates at a slower speed and for these 
reasons the rubber, while being 
worked, will remain upon this roll. 
Here great care must be taken with 
certain compounds especially, for at 
the temperature we have here, vul- 
canization may take place to a certain 
extent. The temperature of both rolls 
in a mill is regulated by turning on 
the hot or cold water and the only 
way the mill man has of judging the 
correct temperature is by the sense 
of touch. " If it feels right " is his 
only guide. There should be some 
way of automatically controlling this 
temperature by means of a thermo- 
stat. Some experimental work might 
be done along this line. 

The compounded stocks from the 
mill room are now allowed to cool to 
age. Then they are taken to the cal- 
ender room. 

Here the stock is put into a ' ' warm- 
ing up mill " of the same type as is 
found in the mill room, the purpose 
being to soften up the stock again so 
that it will pass smoothly and evenly 
through the calender. The calender 
is used to convert the rubber dough 
into sheet form of uniform thickness 
from ^which the majority of rubber 
articles are made. 



Most calenders are of the three roll 
tj r pe. The rubber coming from the 
warming up mill is fed between the 
two upper rolls, passes around the 
middle one, then between it and the 
lower roll, and is removed on the 
opposite side upon a coarse cloth 
known as a " liner," which prevents 
the rubber surfaces from adhering 
together. For sheeting rubber the 
rolls of the calender are run at equal 
rates of speed. 

Where friction is desired, the calen- 
der rolls run at differential speeds. 
This gives the greatest spreading 
effeet. 

The stock, after leaving the calen- 
der, is ready to be made up into the 
articles for which it has been com- 
pounded. 

To follow the rubber from this 
point would mean to outline the 
manufacture of every separate article 
placed upon the market. We have in 
this section simply given a general 
idea as to the handling of rubber in 
its common processes before it goes 
into its specialized uses. We have, 
however, only mentioned the planta- 
tion rubber. The great bulk of this 
rubber without being washed is 
brought to the compound room, put 
into batches, and taken directly to 
the mill room. On account of its pre- 
vious treatment, it may enter the 
manufacturing process without being 
washed and dried in the factory. 




Fig. 38 — Close View of Mixing Mills 



CHAPTER XVIII 
The Principles of Compounding 



In this chapter it will be our aim to 
point out some of the general princi- 
ples of compounding. Some of these 
principles are gained from scientific 
experimenting and some from what is 
commonly called practical experience. 
To say that more has been gained 
through one source than another 
would hardly seem fair, as each has 
profited from the other. 

The art of compounding, for such 
it may be called, has developed in the 
last few years from the point where 
it was purely a rule of thumb to the 
extent that today men are trained in 
the science of compounding. In fact, 
we may go further and say that the 
large expenditure of money in the 
way of equipping laboratories and in 
hiring men to operate them, is sim- 
ply for the benefit of the men who are 
in charge of the compounding. For 
instance, we may find in a laboratory 
several men whose whole time is given 
over to routine work in the test- 
ing of crude rubbers, and for what 
reason 1 That they may turn over 
some valuable information to the com- 
pounders. We find men, too, testing 
the purity of the pigments, again 
to be of assistance to the compound- 
ers. Today we find the large labora- 
tories establishing and prosecuting 
work of a research nature along the 
line of organic accelerators. This, 
again, is done with the idea of gaining 
some knowledge that in the hands of 
their compounders will enable them 
to develop greater speed in curing 
and thus to increase production. The 
expenditure of large sums annually 
for research laboratories is justified 
by the progress made by the com- 
panies which maintain such labora- 
tories. 

It matters not in what particular 



line of work the compounding is be- 
ing done, the same problems are ever 
before the compounder, whether he is 
engaged in compounding tires or toy 
balloons. The following points are all 
to be considered and each given its 
due attention : 

1 — Quality, including tensile 
strength, elasticity, grain, stretch, set, 
hardness, resistance to abrasion, to 
tearing, to cutting, deterioration due 
to ageing. 

2 — Adaptability of stock to the 
processes through which it must pass, 
such as milling, calendering and 
spreading. 

3 — Length of time and conditions 
required for vulcanization. 

4 — Compatibility with other stocks 
with which it is used. 

An excellent example of this is 
found in the different stocks which 
must be developed in the construction 
of a solid tire, where it is necessary to 
produce a stock which will form a 
union with a metal base on one side 
and with the soft vulcanized tread on 
the other: 

5— Color. 

6 — Specific gravity. 

7 — Cost. 

We shall now discuss these points 
as they bear upon compounding in 
mechanical goods, dipped goods, tires 
and hard rubber. 

For the compounding of mechani- 
cal goods, the problem, with the excep- 
tion of a few specials, presents itself 
as follows : The compounder is advised 
of the terms as called for by the speci- 
fications in a contract which includes 
price, delivery, specific gravity, color, 
and usually definite tests to which the 
article must be subjected and pass. 



117 



118 



RUBBER MANUFACTURE 



He will, therefore, take the material 
available and meet the specifications 
with as much margin of quality as the 
price will allow. It is to his advan- 
tage to make the time of cure as short 
as possible in order that the equip- 
ment may render the maximum pos- 
sible production. Otherwise the con- 
ditions are the same as encountered 
in other stocks. 

We shall therefore take each point 
separately for discussion. 

Tensile Strength 

Tensile strength is determined 
mainly by (a) the quality of the rub- 
ber used; (b) the balance between the 
rubber and other compounding in- 
gredients. This embraces all there is 
to be said of compounding for in 
striking this balance, any or all of the 
properties in (1) are developed. 
Tensile strength is acquired mainly 
by the use of zinc oxide and different 
grades of lampblack. Several other 
materials effect tensile strength more 
or less, but these two are in a class 
by themselves. 

Eesistance to abrasion, to tearing, 
to cutting, etc., are very much allied 
to tensile strength, although the latter 
is by no means a measure of them. 



Zinc oxide is, beyond question supe- 
rior to all other materials for obtain- 
ing these qualities, consequently one 
almost never finds a rubber compound 
that does not contain zinc. 

Grain is another close ally of the 
properties just mentioned. It is de- 
sirable to produce a stock which will 
have a grain that is more or less 
knotted up and consequently will pre- 
vent easy tearing. 

With very few exceptions, the ad- 
dition of other compounding ingredi- 
ents to the rubber tend to cut down 
the strength. In the case of certain 
materials, such as inner tubes, sur- 
gical goods, toy balloons, etc., the 
stretch is highly desirable and for this 
reason in their manufacture, very 
little filler may be used. Such as are 
used are mainly employed as color- 
ing pigments. In this connection we 
might mention antimony, iron oxide, 
arsenic yellow, lampblack, litharge, 
and various organic pigments. 

Occasionally where a cheap stock is 
desired, barytes may be used as a 
filler with very little effect upon the 
stretch ; however, in the majority of 
uses for which a rubber compound is 
wanted, high stretch is undesirable. 




Fig. 39 — Stock Bins and Compound Boxes 



THE PRINCIPLES OF COMPOUNDING 



In tires, for instance, too high a de- 
gree of stretch would cause too much 
flexing resulting in inner friction 
which would cause the tire to go to 
pieces in a short time. No rule can 
be given for a proper balance in re- 
gard to this property since it must 
be worked out by actual experiment 
in each individual case. 

Elasticity 

Elasticity is measured inversely by 
the ratio of the work done in stretch- 
ing to the work given back by the re- 
covery. It is difficult to prophesy 
in advance just how a compound will 
conduct itself in this respect, except 
that most cheap fillers, like barytes, 
whiting, etc., have a tendency to de- 
crease this ratio. 

" Set " is nothing but an approxi- 
mate measure of elasticity. 

Ageing Qualities 

The deterioration of rubber articles 
upon ageing is undoubtedly one of 
the most objectionable features. This 
deterioration may be due to several 
factors : 

(a) Cure, either over vulcanization 
or under vulcanization. 

(b) The quantity of sulphur pres- 
ent, either excess or deficit. 

(c) Oxidation, which may be in- 
fluenced by atmospheric conditions 
such as heat, light, humidity, alter- 
nate wetting and drying, gases in the 
atmosphere, or in special cases the 
influence of oils, or other chemicals 
which may come in contact with the 
rubber accidentally or of necessity, as 
in the case where hose is turned to 
conduct acids or oils. Here special 
compounding is necessary to produce 
a more resistant compound. 

By adaptability to working on the 
mill or calender, we mean that the 
compound must not be too soft, 
neither must it be too dry. In cer- 
tain cases precaution must be taken 
to produce stock that will not scorch 
too readily. Again, in the case of 
frictions, it is necessary to produce 
the desired degree of tackiness for 
frictioning. In the tubing machine, 
some stocks may be too dry and thus 
come through rough ; some may swell 
unevenly after coming through the 
die of the tubing machine. Some 



stocks will give trouble due to bloom- 
ing when being calendered. This will 
cause poor unions in case it is used in 
laminated fabrications. Thus if the 
stock is soft, either add some filler or 
remove some of the softeners. If too 
dry the reverse of this will undoubt- 
edly prove the remedy. Mineral rub- 
ber, vaseline, pitches, tar and cheap 
wild rubbers, and vegetable oils may 
be used for these purposes. 

In a large number of cases it is nec- 
essary to cure two or more stocks of 
different nature together. The cure 
of each of these stocks must be regu- 
lated so that both will be cured prop- 
erly during the same length of time. 
"We will take, for example, solid tire 
stocks. Here the volume of rubber is 
so great that there is a tendency for 
the outside to cure more rapidly than 
the inner part unless the time of vul- 
canization is long enough to permit 
the whole mass to acquire the same 
temperature and remain at this tem- 
perature long enough so that the time 
to heat through and to cool off in the 
center will approximately balance. 
Then, again, where tires are vulcan- 
ized by the two-cure process, the car- 
cass gets a fair degree of cure in the 
first heat but must retain the prop- 
erty of holding its shape and at the 
same time that of uniting with the 
tread rubber during the second cure. 
The tread rubber on the other hand 
must take a ' ' set ' ' cure very quickly 
and be able to hold its shape and form 
a union with that already in the car- 
cass. These properties may be ob- 
tained by proper manipulation of the 
sulphur content and by the use of 
suitable accelerators. 
Colors 

The next point is that of color. 
Here the compounder is asked either 
to duplicate a certain stock as to 
color or to produce a stock of certain 
color. This is a point which is most 
important in mechanical goods. Of 
course, the trade may become preju- 
diced in favor of a certain color in 
treads or a certain color of inner 
tubes, but the choice is limited to a 
very few shades, while in the case of 
balloons, variety of tints is to be de- 
sired. The number of colors available 
when only inorganic fillers were used 



RUBBER MANUFACTURE 



restricted the selection very much, but 
today with the use of organic dyes 
many different shades and tints are 
possible. When compounding to 
match a certain shade, one often en- 
counters difficulty for it cannot al- 
ways be foretold just what effect the 
process of vulcanization is going to 
have upon the particular color pig- 
ments which are added, and especially 
is this true of certain organic ones. 

Specific Gravity 

Very often the compounder is asked 
to produce a stock of a certain specific 
gravity. This is done by having at 
hand a knowledge of the specific 
gravities of the different materials 
used in compounding. In this con- 
nection we will give an example. For 
instance, it is desired to produce a 
stock having a specific gravity of 1.59. 
Let us assume that the purpose for 
which this stock is to be used will al- 
low the compounder to use fine Para, 
zinc oxide and sulphur. This is a very 
simple formula but the principle may 
the better be grasped from it. The 
compounder arranges his data in the 
following manner : 

Material Weight 

Fine para 50 

Zinc oxide x = (54.9) 

Sulphur 3 

107.9 



is equal to and the volume of 

5.35 , 

3 

sulphur is equal to = 1.51. Now 

1.98 
the total weight of the compound as 
taken is 50 -j- x -+- 3 = 53 + x and 



its volume 


56.1 4- - 


h 


1.51 = 




5 


.35 






X 






57.61 + 


, and 

5.35 


since 


Vol. = 


Wt. 




Wt. 






Sp. gr. = 


. 


Wt. = 




Sp. gr. 




Vol. 




53 + x ; Volume= 57.61. + 


X 

5T35 


Thus 1.59 (the desired gravity) = 




53 + x 







57 - 61 +5X5 
Therefore x = 54.9 parts of zinc 
oxide necessary to fulfill the above 
conditions. 

Volume Cost 
From the same problem we may il- 

Specific Cost of 

Gravity Volume Cost Weight 

.89 56.1 $.81 $40.50 



5.35 

1.98 



5.35 
1.51 



.10 
.04 



5.49 
.12 

$46.11 



Conclusion 

From his experience he concludes 
that he will use 50 parts of rubber 
with a specific gravity of .89, and to 
cure this three parts of sulphur with 
a gravity of 1.98. The question that 
remains is to determine the amount 
of zinc oxide necessary to give the 
stock a gravity of 1.59. In other 
words, the amount of zinc oxide is 
an unknown quantity, but has a grav- 
ity of 5.35. 

Wt. 

Now the volume = there- 

Sp. gr. 
fore, the volume of rubber is equal to 
50 

— = 56.1. The volume of zinc oxide 
.89 



lustrate ' what is meant by volume 
cost in compounding. Filling in the 
costs and quantity of zinc oxide in 
our data we find that 107.9 pounds of 
this stock will cost today $46.11, 
therefore, the cost of one pound will 
be $.427. This stock has a gravity 
of 1.59, therefore, a cubic foot of it 
will weigh 62.4 (a cubic foot of water) 
times 1.59 or 99.216 pounds. We 
have already determined the cost per 
pound to be $.427, therefore, the cost 
of a cubic foot or volume cost, as it 
is termed, will be $.427 times 99.216 
or $42.36. 

From the above example the 
method of compounding with refer- 



THE PRINCIPLES OF COMPOUNDING 



121 



ence to cost will also be illustrated. 
If the volume cost must be necessarily 
low, then cheap rubber and pigments 
must be used. If on the other hand, 
quality is not to be sacrificed for cost, 
then better materials may be em- 
ployed. In this connection, however, 
a compounder is able to save large 
sums of money for his company, 
where he is able to produce a quality 
equal to or better than their com- 
petitors at a lower volume cost. Ex- 
perience here is a valuable asset. A 
wide experience and knowledge of 
fillers and rubbers, with a clear un- 
derstanding as to what may be ac- 
complished with each one, constitutes 
the requisite for a good compounder, 
feet us point out just a few of the 
many troubles that must be guarded 
against. First, some dirt may get 
into the compound, either through the 
fillers in their handling, or in the rub- 
ber itself, and as a result many dol- 
lars' worth of goods may be lost. This 
is especially true in the case of com- 
pounds which contain a high rubber 
content, like tubes or band stock. The 
rubber will not adhere to the dirt 
particles during vulcanization, and 
when finished and the rubber is 
stretched it separates from the for- 
eign body and this leaves a hole and 
weakens the goods at this point. 

Second, moisture to any extent in 
any of the materials used in a stock 
is very objectionable. If moisture 
is present when the stock goes into 
the vulcanizers and is heated above 
the boiling point of water, this en- 
closed moisture will exist in the gase- 
ous condition and cause " blowing " 
or the making of the stock porous. 
Again, it may come out toward the 
sirrf ace and there cause ' ' blistering ' ' ; 
again, it may discolor white stocks, 
and, again, if present in fabric, it will 
cause poor unions in tire construc- 
tion. 

Third, if the fillers contain any 
lead compounds or the batch pans 
from a previous stock, and these hap- 
pen to find their way into what is 
supposed to be a white compound, 
they will discolor it. 

Fourth, great care must be exer- 
cised and close vigilance kept of what 
is going on in the compounding room. 



Should the wrong kind or the wrong 
amount of material be used or a cer- 
tain material be left out of a com- 
pound, it will be liable to throw that 
stock out in cure, color and gravity, 
thus rendering it unfit for the pur- 
pose for which it was to be used. 

Scorching 

Fifth, scorching on the mixing 
mills, calender or tube machines is 
usually due to forcing the stock to 
run faster than it should, too high 
temperature, too much speed or in- 
sufficient warming up. Quick cur- 
ing stocks especially suffer from these 
causes. The best way to get them 
plastic so that they will run through 
other processes more easily, is to work 
thoroughly on the mixing mills before 
any powders are added, or, in other 
words, be sure the rubber is well 
broken down. 

Sixth, what is termed " tough 
stock " is generally caused from in- 
sufficient milling of the rubber be- 
fore adding the fillers. Then, too, 
some compounds have a tendency to 
toughen on long standing. Some 
stocks may come off from the mill in 
good condition, but before the heat, 
caused in mixing, has had time to 
radiate out, the rubber will be piled 
in bins, thus trapping the heat, and 
there will take place a certain degree 
of -vulcanization. The result is simi- 
lar to tough stock, but is really a 
scorched condition. 

Seventh, a lumpy stock may be pro- 
duced in several ways. For instance, 
the presence of dirt, as mentioned 
above, may cause it; or lumps which 
occur in shoddy which has not been 
evenly reclaimed or refined ; then, too, 
the mixing of tough stock or scorched 
stock with a soft compound may be 
responsible. 

Eighth, sulphur bloom on uncured 
stock, such as friction and cover 
stock, may be due to using tough or 
scorched stock, insufficiently ' ' warmed 
up " stock, too high a temperature 
on the calender, and, under some con- 
ditions, too low a temperature. 

Ninth, poor union of stocks may be 
due to some incompatibility of the 
stocks to be joined, improper prepa- 
rations of stock in mill rooms, dirt, 



RUBBER MANUFACTURE 



moisture, soapstone, or anything 
which may affect the tacky surface of 
the rubber, incompletely dried ce- 
ment, or poor local workmanship. 

Tenth, porosity of the cured stock 
may be due to moisture as mentioned 
above, insufficient pressure, under 
cure, or improper compounding. 

Eleventh, surface pitting is closely 
related to porosity or blowing, and is 
caused by air trapping, surface mois- 
ture, or perhaps the same causes 
which produce porosity. 

Twelfth, improper cure is a thing 
which must be closely watched. If a 
sample is over-cured it cannot be 



brought back, for the process of 
vulcanization is not reversible, as 
pointed out when we discussed re- 
claiming. Over-cured stock may or 
may not lack in tensile strength, but 
it always lacks in stretch, is always 
short grain and ages very poorly. On 
the other hand, under cure lacks in 
tensile strength, resiliency and gener- 
ally in aging properties. Therefore, 
the vulcanizing must be closely 
checked. 

Thirteenth, as mentioned above, it 
is difficvdt to match certain shades of 
color due to variations of materials 
used. 



CHAPTER XIX 
Chemical Analysis of Manufactured Rubber 



In this chapter we shall aim to out- 
line only methods which may be of 
some pi-aetical use to men in the lab- 
oratories. We shall not attempt to 
go into the subject to the extent of 
the complete analysis of a sample of 
rubber, but shall sketch methods for 
the determination of facts which the 
man in charge of the laboratory is 
anxious to have in the way of control 
work. 

The first thing necessary is to ob- 
tain a fair sample of whatever mate- 
rial is to be examined. What was 
said in a previous article dealing with 
the chemical analysis of crude rub- 
ber in regard to the obtaining of a 
sample applies here as well. Very 
often the stock furnished is composed 
of but one mix and in such cases it 
is a fairly easy task to obtain a uni- 
form sample. However, when the 
sample submitted is composed of sev- 
eral different mixes and these have 
been vulcanized, thus forming a com- 
pact mass, the problem is a more dif- 
ficult one. As an example of the 
former instance, we have such stocks 
as inner tubes which are- very easily 
sampled, while as an example of the 
latter, we have the casing of an auto 
tire. Here we have a certain mix for 
the bead, another for the friction, an- 
other for the sidewalk another for the 
tread, and still another for the cush- 
ion or breaker. In the latter case, the 
chemist must take a knife and scissors 
and proceed to dissect the sample, tak- 
ing out the different portions which 
represent different mixes. It takes 
some time and experience to obtain 
good samples of the friction espe- 
cially. 

Procedure of Analysis 

We shall now outline the general 
procedure of analysis, assuming that 



the sampling has been carefully done. 

It is never necessary to analyze 
manufactured rubber for moisture. 

The analysis may be divided into 
two parts, both of which may be run 
by the chemist at the same time, the 
one dealing with the organic mate- 
rials present and the other with the 
inorganic. 

Determination of Organic Content 

For the examination of the organic 
content, we take advantage of the 
action of different solvents thus re- 
moving certain materials by extrac- 
tion methods. 

To allow the use of such practice 
the sample must first be reduced to a 
finely divided state so that the sol- 
vent exercises its maximum effect. 
This is accomplished either by run- 
ning the sample through a digester, 
if it is of a nature to allow this treat- 
ment, oi', as in the case of ebonite, it 
may be filed ; but very often it is nec- 
essary simply to cut the sample into 
as small pieces as possible with the 
scissors. 

The first solvent which is employed 
in determining the organic portion is 
acetone. The acetone used for this 
purpose should be colorless, and if 
it has colored upon standing it should 
be redistilled over potassium carbo- 
nate before being used. 

A weighed sample of the finely 
divided rubber is placed in an extrac- 
tion thimble of the desired type. We 
prefer a Baile3 r -Walker which is pro- 
vided with a Wiley block tin con- 
denser. The thimble is then placed 
in position and the rubber extracted 
with hot acetone for a period of ten 
hours. Some have contended that ten 
hours is not a sufficient length of 
time, and, of course, it is not for ebo- 



123 



124 



RUBBER MANUFACTURE 



nite, but for the vast majority of 
eases it is perfectly safe and where 
exceptions come the analyst must use 
his own judgment as to the proper 
length of time. During the extraction 
the operator should note frequently 
the general appearance of the extract. 
If the extract slowly turns yellow 
and has a slight fluorescence it indi- 
cates the presence of bitumens, while 
if it is strongly fluorescent, it indi- 
cates coal-tar pitch. Mineral oil mani- 
fests itself here also by making the 
extract fluorescent yet it does not 
color it to any extent. 

When the extraction is completed, 
the extract is allowed to cool and care- 
fully observed, for some materials are 
soluble m hot acetone but crystallize 
out on cooling. This is true of paraf- 
fin. The separation of oily drops 
generally indicates factice. The ex- 
tract is now evaporated over a water 
bath to dryness in a weighed con- 
tainer. Here is the advantage of the 
extraction apparatus mentioned above 
— the flask is of such size and shape 
that it can be weighed and the ex- 
tract evaporated to dryness in it, 
while if a Soxhlet apparatus has been 
used it is customary to transfer the 
extract to a smaller tared dish for 
evaporating. This introduces the pos- 
sibility of loss and also the waste of 
acetone in washing while transferring 
from one flask to another. 

When evaporating to dryness, if 
there is very much free sulphur pres- 
ent, toward the end of the process 
there is liable to take place very vio- 
lent pounding and thus the loss of 
some of the residue on account of its 
being spurted out. This may be over- 
come to some extent by the addition 
of a little benzene when the evapora- 
tion- will continue quietly to dryness. 
When the evaporation is complete the 
flask is dried in an oven. Some chem- 
ists have recommended that the flask 
be dried in a hot air oven for an hour 
at 110 deg. C. while others claim that 
it is better to dry for three hours at 
60 deg. C. The latter is the practice 
in this laboratory, for we have found 
that some of the rubber resins are 
volatile at 110 deg. C. When dried 
this is weighed and thus the total 
acetone extract is determined which 



in itself is of little value. In this 
residue is to be found the free sul- 
phur, resins, oils either mineral or 
fatty, and paraffin. In addition to 
these there will be the acetone soluble 
part of the factice, or reclaim, or 
bitumens and pitches which might 
have been used in the rubber stock. 

Determination of Sulphur 

The first component in the acetone 
extract to be determined is sulphur. 
Many methods have been suggested 
and much discussion has been given 
to this particular subject. However, 
from a practical standpoint, the fol- 
lowing method or methods give ac- 
curate enough results for control 
work at least. 

The weighed residue in the flask in 
which we carried out the extraction, 
is covered with dilute nitric acid 
(1-1) and a cover glass placed over 
the mouth of the flask, while it is 
warmed over a water bath. Care 
must be taken here that the reaction 
is not too violent, for if such should 
happen, some of the sulphur might 
be lost. After the first reaction is 
over about 5 c.c. of a saturated 
solution of potassium chlorate is 
added and the solution allowed to 
heat over the water bath until the sul- 
phur and the organic matter has all 
disappeared. In some places the po- 
tassium chlorate is added in the crys- 
talline form, but it is our experi- 
ence that it is much more effective as 
an oxidizing agent here if it is first 
dissolved and its solution is added. 
The length of time required for the 
complete oxidation varies a great 
deal and the only safe procedure is 
to judge from the appearance of the 
flask. In same cases additional nitric 
acid must be added and this may be 
the concentrated. In some instances 
where oxidation seems to be very dif- 
ficult, we often make additions of 
fuming nitric acid. This will gener- 
ally complete the oxidation in a short 
time. The solution is then evaporated 
to dryness over a water bath, or to a 
syrup if that is as far as it will go. 
There is no danger of losing any of 
the sulphur by the volitization of the 
sulphuric acid over a water bath, 
as the sulphur now exists largely as 
the sulphate of potassium due to the 



CHEMICAL ANALYSIS OF MANUFACTURED RUBBER 



fact that potassium chlorate has been 
added. The residue is now taken up 
in water to which a little hydrochloric 
acid has been added, and if a clear 
solution does not result it is filtered 
while cold. The filtrate is then 
brought up to boiling and before add- 
ing the barium chloride, which is the 
customary procedure, we are indebted 
to A. G. Carlton for a slight modifica- 
tion which we have found to work 
beautifully and which causes the 
barium sulphate to settle very rapidly 
in a granular form which will allow 
of its filtration in thirty minutes' 
time. 

Barium Sulphate Troubles 

m If to the hot filtrate containing the 
sulphate you add 10 c.c. of a satu- 
rated water solution of picric acid 
and then the barium chloride drop at 
a time, then allow it to stand until it 
has settled your troubles with barium 
sulphate will be eliminated. The pic- 
ric acid washes out from the barium 
sulphate very easily. The sulphur is 
then determined in the usual manner, 
by burning off the carbon of the filter 
and igniting until white. The sul- 
phur is obtained by multiplying the 
weight of the barium sulphate by 
0.1373. 

We have oxidized the sulphur in 
the acetone extract by the use of 
nitric acid and bromine and obtained 
very good results. It has been 
claimed that in order to oxidize all 
the free sulphur, in the presence of 
these organic substances, in addition 
to its nitric acid treatment the resi- 
due left upon evaporation should be 
fused with a mixture of five parts of 
anhydrous sodium carbonate and 
three parts of potassium nitrate. For 
work of a research nature this might 
be necessary, but not for the work 
in a commercial laboratory. 

Some volumetric methods have been 
suggested but we shall not take the 
space here to outline these but refer 
to the Thiocyanite method of C. 
Davis and J. L. Foucar, Jon?- Soc. 
Chem. hid. 31 (1912), p. 100. 

Determination of Mineral Oil. Vaseline and 
Paraffin 

The estimation of mineral oil, vase- 
line and paraffin is not carried out 



quantitatively very often. As stated 
above the appearance of the acetone 
extract furnishes a clue as to their 
presence and in actual work a man's 
knowledge of the stock gives an idea 
as to the amount of these materials 
which might be used. Where it is de- 
sired to make their determination, it 
is necessary to extract a new sample 
with acetone and to use the extract 
for the determination. The method 
consists in destroying all the other 
substances in the extract except the 
paraffin compounds by the use of 
concentrated sulphuric acid. To ac- 
complish this, 2 c.c. of concentrated 
sulphuric acid are added to the ex- 
tract in the extraction flask, covered 
with a watch glass and heated in an 
oven for from three to four hours at 
a temperature of 110 deg. C. The 
contents of the flask are then ex- 
tracted with petroleum ether several 
times and the washings transferred to 
a tared flask after having been shaken 
up in a separating funnel with a soda 
solution containing some alcohol. 
The petroleum spirit is then evap- 
orated off and the flask is dried in an 
oven for two to three hours at 110 
deg. C, then weighed and its percent 
determined. 

The other components in the ace- 
tone extract are difficult of deter- 
mination and really do not add very 
much to the knowledge of the sam- 
ple under consideration. 

Some chemists have led us to think 
that by a determination of the rub- 
ber resins in the acetone extract it is 
possible to say what variety of crude 
rubber is used in the stock. This 
may be true in a certain few cases 
where the resins have a peculiar odor 
which identifies them, but it is not 
general enough to be dependable. 

The next general procedure is to 
gain some idea as to the amount of 
bitumens and pitches. The appear- 
ance of the acetone extract, as already 
stated, gives us a qualitative test as to 
whether or not these substances are 
present ; but if there is a question as 
to their actual existence in the sample, 
the following test may be applied : 

Either some of the fresh sample 
or some of the acetone extracted is 
placed in a test tube and covered over 



126 



RUBBER MANUFACTURE 



with carbon disulphide, and if either 
bitumens or pitches are present, they 
will be dissolved and color the solu- 
tion ; then by use of pyridine as a sol- 
vent you may distinguish between the 
two as it is a solvent for the pitches 
but not for bitumens. 

If either of these are found to be 
present the residue left in the thimble 
from the acetone extraction is dried 
by allowing it to remain out in the 
air when the acetone will soon evap- 
orate, then placed in an extraction 
apparatus and extracted for several 
hours with carbon disulphide ; four 
hours is generally sufficient. The ex- 
tract is then distilled and the residue 
dried in an oven three hours at 110 
deg. C. and the weight of the residue 
determined. This will not represent 
all of the bitumens or pitches as part 
appeared in the acetone extract; in 
fact tli is extraction will contain from 
ten to thirty per cent of the total 
amount in the original stock. It is 
plain therefore that this determina- 
tion is of value only to the extent of 
giving us a general idea as to the 
amount of these substances present. 
Here again a man's judgment and 
experience must fill in the rest. 

Determination of Rubber Substitute 

The last experiment, which is made 
upon the sample for its organic eon- 
tent, is to ascertain a knowledge of 
the factice or rubber substitute 
present. 

To carry out this advantage is 
taken of the behavior of these sub- 
stances with alkalies. Under the chap- 
ter dealing with rubber substitutes, 
we pointed out the fact that these 
materials were saponifiable. 

To carry out this test successfully 
the rubber must be in a very finely 
divided state for the penetrating 
power of the alcoholic potash solution 
is very small. 

The residue left in the thimble 
from the carbon disulphide extraction 
is dried and in some cases may lo re- 
duced to a fine powder. It is then 
transferred to a flask, preferably one 
which has a ground glass connection 
with a reflux condenser. Then there 
is poured over the rubber the alco- 
holic solution of potash. Some lab- 



oratories use a N/5 solution, others 
N/1, and some N/2 solution. The 
more concentrated the solution, the 
smaller the amount needed. The rub- 
ber is now boiled in this solution over 
a water bath for about three hours 
when all of the substitutes should 
have saponified and colored the so- 
lution to some extent, depending of 
course as to whether brown or white 
factice has been used. Prom this 
point two procedures have been used 
and are in use in some places today, 
although the one is subject to grave 
criticism. 

We shall outline the better method 
first. In this the solution is poured 
off from the rubber into a flask and 
the rubber is then washed three or 
four times by boiling it up with 20 
c.c. of water, each portion being 
added to the flask in which the origi- 
nal solution is contained. The com- 
bined solutions are then evaporated 
over a water bath to a volume of 
about ten or fifteen cubic centimeters. 
This clear solution which contains the 
soap from the saponification of the 
substitutes is then transferred to a 
separately funnel, and when cold 
acidified with either hydrochloric or 
sulphuric acid when the correspond- 
ing fatty acids will be liberated from 
the soap. These are extracted with 
ether three or four times and the 
ethereal solution evaporated in a tared 
flask, and dried at 110 deg. C. for 
an hour. The weight and thus the 
percent of factice removed by this 
treatment is then determined, but it 
must be remembered that part of the 
factice was removed by the acetone 
extract; also that we are weighing 
here the organic acid and not the fac- 
tice itself, therefore a correction must 
be made. To apply this correction, 
it must be determined whether white 
or brown factice was used and to 
ascertain this a test is made for 
chlorine in the alcoholic potash ex- 
tract. If it is present, white factice 
was used; otherwise it was the brown 
substitute. To correct, therefore, for 
the white factice, the amount of or- 
ganic acid is multiplied by 1.136, and 
if chlorine is absent, thus indicating 
the brown, multiply by 1.064. This 
final amount of factice also falls short 



CHEMICAL ANALYSIS OF MANUFACTURED RUBBER 



of the amount actually used in the 
compound by the amount that was 
dissolved by the acetone extract. So 
by experiment it is necessary to make 
another correction and if brown sub- 
stitute was used the amount found is 
increased by one-fourth, and needless 
to say this same amount should be 
subtracted from the acetone extract. 
If white factice was used, then an ad- 
dition of one-ninth is necessary. 

The alternate method for factice 
determination consists in thoroughly 
drying the residue in the thimble left 
after the carbon bisulphide and 
weighing it. Then subject it to the 
same alcoholic potash treatment as 
mentioned above in exactly the same 
manner. After effecting the saponi- 
fication, the rubber is filtered on 
a tared paper, washed with boiling 
water several times before being 
transferred to the filter, then dried 
and weighed. Its loss in weight is 
taken as being the saponifiable part 
and thus calculated as factice. This 
method leads to poor results, due to 
the fact that it is very difficult to 
wash out of the rubber the last traces 
of the alkali, but worse than this, we 
know that many fillers are soluble in 
strong alkali and parts of these will 
be removed and thus be calculated as 
substitutes. Such fillers as lead, an- 
timony and zinc all behave in this 
manner. 

There are certain instances where 
it is suspected that both white and 
brown substitutes have been used in 
the compound. To determine this 
fact a new alcoholic extraction must 
be made and the extract is then evap- 
orated to dryness; 1 c.c. of water is 
added and then more heat is applied 
when the majority of the organic 
matter will be destroyed. By the use 
of a spatula, sodium peroxide is 
gradually added with continued heat- 
ing until the whole melts. The 
mass is then allow-ed to cool and is 
taken up in water and made up to a 
definite volume. This is divided and 
in one portion chlorine is determined 
and in the other sulphur. For the 
chlorine determination, the solution 
is acidified with nitric acid and the 
chlorine precipitated and determined 
bv the addition of silver nitrate. 



The other portion is acidified with 
hydrochloric acid and the sulphur 
estimated by the addition of barium 
chloride in the manner outlined 
above. The percentages of sulphur 
and chlorine in white substitute do 
not vary much so that it is safe to 
calculate for the amount of chlorine 
present the corresponding amount of 
sulphur and the excess sulphur pres- 
ent is a measure of the amount of 
brown substitute used in the com- 
pound. 

Determination of Rubber Content 

This finishes the analysis of any 
sample for its organic content with 
the exception of the caoutchouc hy- 
drocarbon itself. Considerable work 
has been done with the idea of finding 
some method by means of which the 
rubber proper might be determined, 
but at present none of the methods 
suggested allow of its accurate de- 
termination. 

The general practice is therefore 
to arrive at the rubber content by 
difference. This method is subject to 
criticism if the inorganic matter pres- 
ent is determined by ashing the sam- 
ple, for during this treatment some 
of the components are changed chemi- 
cally and some may even be vola- 
tilized. 

But now we are able to determine 
the inorganic matter by the use of 
solvents whereby the rubber is dis- 
solved and washed away from the 
pigments with the aid of centrifugal 
machines. 

The true rubber content is then ar- 
rived at by adding together the per- 
centage of the various extracts, the 
sulphur added for vulcanization and 
the inorganic matter and subtracting 
this total from 100. This method has 
the disadvantage that it places all 
the errors in the previous work upon 
the rubber content, and yet it gives 
results acctirate enough for commer- 
cial work. In some cases the caout- 
chouc may be determined by the tet- 
rabromide method as modified by 
Spence. But too many other factors 
come in to cause trouble for it to be 
regarded as a reliable method. 

The nitrosite method proposed by 
Harries and Alexander is too long 



128 



RUBBER MANUFACTURE 



and too tedious a method to recom- 
mend itself, especially when the re- 
sults are somewhat questionable. 

Having dealt in the last section 
with the organic portion in a sample 
of manufactured rubber, we shall 
now proceed with the inorganic part. 

Determination of Sulphur 

The first component to be con- 
sidered is sulphur and it bears a very- 
important part. We have pointed 
out the determination of the free sul- 
phur as it was found in the acetone 
extract but in manufactured rubber 
we must also know the amount of 
combined sulphur. By this we mean 
the amount of sulphur in combina- 
tion with the caoutchouc itself, for in 
addition to this we have sulphur in 
combination in the fillers used, as in 
the case of antimony, which is really 
only present in the form of the sul- 
phides of antimony, and in the case 
Of lead sulphide which is formed dur- 
ing vulcanization when litharge is 
used in the compound, in lithopone, 
as sulphur in zinc sulphide, and also 
here as the sulphate of barium. Sub- 
limed lead also has sulphur in the 
form of lead sulphate. Then again 
we have the sulphur which exists in 
factice or rubber substitutes, and a 
little in mineral rubbers. These rep- 
resent some of the places in which we 
may expect to find sulphur. 

With these facts in mind we pro- 
ceed to determine the coefficient of 
vulcanization or degree of vulcaniza- 
tion. To obtain this knowledge, we 
must determine the total combined 
sulphur in the sample which we will 
represent by x; the total sulphur 
which is in combination with inor- 
ganic substances which we will desig- 
nate as y; then the expression (x-y) 
will equal the amount of sulphur in 
combination with the rubber proper. 

The formula then which represents 
the degree of vulcanization is repre- 
sented thus V = 1Q0 ( x -'-l) where V - 

degree of vulcanization, z = amount 
of caoutchouc, which is generally de- 
termined by difference. This as was 
pointed out before is liable to an error 
of several per cent. 



To determine the x, or the totally 
combined sulphur, it is necessary to 
use a sample which has been subjected 
to all of the extractions, the acetone 
removing the free sulphur, the car- 
bon bisulphide removing a small 
amount of sulphur as it occurs in the 
mineral rubbers, and the alcoholic 
potash removing the sulphur found in 
factice. 

For this assay many methods have 
been suggested but we shall outline 
only a few of these. 

First a weighed amount of the rub- 
ber is placed on the crucible and cov- 
ered with a watch glass and some 
concentrated nitric acid is added. 
When the violent reaction is over the 
watch glass is removed, and the solu- 
tion is evaporated to dryness over 
water bath. In case there are some 
rubber particles still remaining, the 
nitric acid treatment is repeated. To 
the contents of the crucible a fusion 
mixture of sodium carbonate and po- 
tassium nitrate is added and when 
thoroughly mixed is covered and very 
gradually heated. When the reaction 
takes place it gives off a considerable 
amount of energy and therefore the 
reaction may be rather violent. 
When this is over the temperature is 
raised and the whole mass brought to 
a quiet fusion and held there until it 
appears homogeneous. In some cases 
the fusion is poured out on an iron 
plate and when cold is lixiviated with 
water along with what remains on 
the crucible. It will be necessary to 
filter this solution for it will have sus- 
pended in it the carbonates of the 
different metallic fillers used. The 
filtrate is acidified with hydrochloric 
acid and evaporated to dryness, taken 
up with a little hydrochloric acid and 
water and again filtered if necessary. 
The sulphate is then determined as 
outlined before. 

In this test as in all others, blank 
tests should be run with the chemi- 
cals to make sure they are all free 
from sulphur. 

Another method which does not 
take a long time and gives good re- 
sults is the following : 

About fifteen grams of potassium 
hydroxide are placed in an iron or 



CHEMICAL ANALYSIS OF MANUFACTURED RUBBER 



nickel dish with two c.c. of water and 
heated until it is dissolved, then a 
weighed amount of rubber which has 
been extracted is added and the heat- 
ing is continued. Smoke will be 
given off and there will be a little 
sputtering which always comes when 
the mass is being stirred. The mass 
turns black, due to the charring of 
the rubber and now sodium peroxide 
is added in small portions until the 
whole mass comes into a quiet state 
of fusion and the carbon disappears. 
The contents cf the dish are allowed 
to cool and then taken up in water 
and acidified with concentrated hy- 
drochloric acid until the iron oxide, 
which comes from the action of the 
fusion upon the dish, has dissolved. 
If there remains a white precipitate 
it is probably barium sulphate and 
it may be filtered off and weighed 
thus getting the sulphur in it. The 
filtrate is treated for sulphur in the 
usual manner ; then the two are added 
together. Very often when barium 
sulphate is precipitated in the pres- 
ence of iron salts there results con- 
siderable adsorption of the iron with 
the result that when the barium sul- 
phate is ignited it is colored yellow or 
even reddish brown. In such a case 
the contents of the crucible are dis- 
solved in concentrated sulphuric acid, 
with the aid of heat if necessary, 
and then the solution is poured into 
a beaker of water when the barium 
sulphate will reprecipitate, is filtered 
out and ignited again when it will be 
white. 

The methods mentioned under free 
sulphur have been used here also — 
namely oxidizing with concentrated 
nitric acid aided either by potassium 
chlorate or bromine. But these 
methods are not applicable if an in- 
soluble sulphate like barium is pres- 
ent. These are the methods used most 
frequently. 

The ij in the above formula or 
the combined inorganic sulphur is 
determined as follows: A weighed 
amount of the residue obtained by 
dissolving away the rubber from the 
charge, as will be outlined below, is 
placed in an iron dish with about five 
grams of potassium hydroxide and 
then boiled down and oxidized with 



sodium peroxide as outlined above. 
The mass is dissolved in water, acidi- 
fied with hydrochloric acid and the 
process is continued as outlined 
above. This will give the sulphur 
inorganically combined which taken 
from the totally combined sulphur 
gives the amount in union with the 
caoutchouc which multiplied by 100 
and divided by the amount of caout- 
chouc gives the degree of vulcaniza- 
tion. 

Analysis of Mineral Matter 

For the analysis of the mineral 
matter which was put into the com- 
pound the old incineration method is 
unreliable. 

The best method today consists in 
placing from 0.5 to 1.0 gram of the 
rubber in a weighed centrifuge tube 
about five inches long and an inch in 
diameter. The rubber is then treated 
with from 10 to 15 c.c. of a distillate 
obtained from petroleum having a 
boiling point around 200 deg. C. or 
a little higher. The tube is fitted 
with an air condenser about two feet 
long and then heated in a paraffin 
bath so that the solvent just boils. 

The length of time necessary to dis- 
integrate the rubber varies consider- 
ably. Where the degree of vulcani- 
zation is low a few minutes will be 
sufficient, but, as the degree of vul- 
canization goes higher, the time re- 
quired to effect solution is longer. As 
the rubber approaches ebonite, this 
method becomes impossible. 

When the solution is complete it is 
allowed to cool, when the mineral 
matter will settle and the supernatant 
liquid is decanted. The mineral resi- 
due is then washed with light petro- 
leum spirit and the tube placed in a 
centrifugal machine and centrifuged 
until the supernatant liquid is free 
from solid particles. In the majority 
of cases this requires from twenty to 
thirty minutes, and at the end of this 
time the mineral matter is a hard 
compact mass which allows the liquid 
to be poured or siphoned off 
without loss of residue. This wash- 
ing is repeated several times and each 
time the residue must be broken up 
with a spatula to enable effective 
washing. The residue is then dried 



130 



RUBBER MANUFACTURE 



to constant weight and the per cent of 
mineral charge thus ascertained. 

The reason that we use the centri- 
fuge tubes from the beginning is that 
it saves transferring the solution 
which gives considerable chance for 
error. 

From this point on we proceed al- 
most, as though we were carrying out 
an inorganic analysis. First, how- 
ever, we must carefully inspect the 
mineral charge, for there may be in 
it fiber, lamp black, etc., and these 
along with other materials may be 
identified by an examination with a 
magnifying glass. Also before taking 
portions for analysis the whole resi- 
due must be carefully ground and 
mixed because the process of centri- 
fuging has divided it into a more or 
less stratified condition, the heaviest 
fillers being thrown out first and tbe 
lightest, ones last. 

A weighed portion of the residue 
is now placed in a beaker or evap- 
orating dish and treated with dilute 
hydrochloric acid. Note whether any 
CO. or H„S is given off. The solu- 
tion is evaporated to dryness over a 
water bath and the residue moistened 
witli concentrated hydrochloric acid, 
again evaporated to dryness and then 
heated in an oven at 110 deg. C. for 
one hour. Moisten the residue again 
with hydrochloric acid, then add 200 
c.c. of water and bring to boiling, 
then filter on a tared paper. If 
there is a large amount of lead pres- 
ent, it may be necessary to boil up the 
residue with more distilled water, fil- 
ter and combine the filtrates. The 
residue is dried and weighed. It 
may contain barium sulphate, silica, 
carbon, and organic matter. The resi- 
due is then ignited and weighed. In 
the majority of cases, this ignition 
loss is a fairly good indication as to 
the amount of carbon present unless 
the silica runs high, as determined 
later, in which case part of the loss 
is due to water. 

The residue is now placed in a 
platinum dish, if it was not ignited in 
one, moistened with hydrofluoric acid 
and a drop of sulphuric acid added, 
then evaporated to dryness over a 
water bath, ignited and weighed. 
The loss in weight here, of co\irse. 



represents the silica, and the residue 
the barium sulphate. In some cases 
this residue is colored reddish brown 
due to the presence of iron which may 
be elhninated as pointed out above. 
Sometimes the residue is fused with 
an alkaline fusion mixture and then 
analyzed in the usual manner. Thus 
the barytes and siliceous materials are 
determined. 

The filtrate from the acid-insoluble 
is acidified with hydrochloric acid and. 
as far as rubber fillers are concerned, 
when hydrogen sulphide is conducted 
into this solution we expect to see 
either a black sulphide of lead form, 
or an orange one of antimony. Our 
idea as to which one is pretty well 
fixed also for if the original sample 
was gray or black we expect lead, 
while we expect to see the antimony 
if the stock was red. Of course there 
are times when the above reasoning 
does not hold. 

The hydrogen sulphide precipitate 
is dissolved in nitric acid, then a lit- 
tle sulphuric acid is added and 
the solution evaporated until fumes 
of sulphuric acid appear. The solu- 
tion is then cooled, 75 c.c. of water 
and 25 c.c. of alcohol added, and 
allowed to stand an hour when 
the lead sulphate may be filtered off. 
washed with water containing alco- 
hol, ignited and weighed as lead sul- 
phate. 

Some volumetric methods for de- 
termination of lead may also be used. 

The antimony sulphide is washed 
into a weighed crucible and nitric acid 
added, then evaporated to dryness 
over a water bath. Fuming nitric 
acid is then added, evaporated again, 
then gently heated and finally ignited 
and weighed as SbO... 

If other sulphides beside antimony 
are thrown out of the acid solution by 
hydrogen sulphide, they may be sepa- 
rated by the use of sodium sulphide. 

The filtrate from the sulphides which 
is acid with hydrochloric acid and 
also contains some hydrosulphuric 
acid, which during the hydrogen sul- 
phide precipitation has reduced the 
iron, if any is present, to the ferrous 
state, is boiled to remove the hydro- 
gen sulphide and nitric acid is added 



CHEMICAL ANALYSIS OF MANUFACTURED RUBBER 



to oxidize the iron. During this boil- 
ing there will be a separation of sul- 
phur which must be filtered out. 
Some ammonium chloride is then 
added and the hot solution made alka- 
line with ammonium hydroxide. The 
precipitate which forms is composed 
of either the hydroxide of iron or that 
of aluminum, or perhaps both. A 
good idea of this is judged from its 
color. 

The solution is filtered. The resi- 
due is ignited and weighed as AL0 3 
or Fe„0 3 . When it is necessary to 
actually determine the amount of iron 
and aluminum., that is done in the 
usual manner by dissolving out the 
ALO. with sodium hydroxide. The 
filtrate from the iron group is made 
alkaline with ammonium hydroxide 
and the zinc precipitated as sulphide. 
The sulphide of zinc is very difficult 
to filter, but if the ammoniacal solu- 
tion is warmed and hydrogen sulphide 
conducted into it, it comes down in a 
form which filters comparatively easy 
for zinc. After the zinc sulphide is 
filtered out and washed it is dissolved 
off the filter paper with hydrochloric 
acid into a weighed crucible. The 
solution is then evaporated over a 
water bath, freshly precipitated mer- 
curic oxide is added, carefully heated 
and ignited to constant weight, thus 
giving the amount of zinc oxide. 

The zinc is easily determined volu- 
metrieally by dissolving the zinc sul- 
phide in dilute hydrochloric acid and 
titrating it with a solution of potas- 
sium ferrocyanide. which has been 
standardized against a known zinc 
chloride solution, using uranyl nitrate 
as an external indicator. This gives 
very good results. 

The calcium in the filtrate from the 
zinc is determined by adding ammo- 
nium oxalate to the hot solution. The 
calcium oxalate is filtered off. washed, 
ignited to constant weight and deter- 
mined as calcium oxide. The mag- 
nesium left after removing the cal- 
cium is precipitated in the cold solu- 
tion by adding disodium hydrogen 



phosphate and proceeding in the 
usual manner. 

Determination of Carbon or Graphite 

It is weighed as Mg..P.,0 T and 
then calculated to MgO. This consti- 
tutes the general procedure of analy- 
sis of a sample of manufactured rub- 
ber. 

As amorphous carbon and graphite 
are used in large quantities their de- 
termination is sometimes required. 

One or two grams of the original 
rubber is placed in an evaporating 
dish and covered with nitric acid, the 
dish being covered with a watch glass 
until the first reaction is over, then 
the solution is evaporated to dryness 
over a water bath. If any rubber re- 
mains the process is repeated. When 
the rubber has all disappeared, the 
residue is washed into a large beaker 
and boiled up with 400 c.c. of water. 
The solution is then filtered through 
a tared filter, washed several times 
with hot water, then transferred to a 
beaker and boiled up with dilute am- 
monium hydroxide to which a small 
amount of ammonium chloride is 
added. The solution is again filtered 
through the original tared filter paper 
and washed with water. The residue 
is again transferred to a beaker and 
this time boiled up with dilute hydro- 
chloric acid, filtered upon the tared 
filter, washed, dried and weighed. 

This residue may contain mineral 
matter which was insoluble in nitric 
acid, ammonium hydroxide and hy- 
drochloric acid. For instance, bary- 
tes and silica will both withstand this 
treatment. So the residue is now 
ignited and the carbon burnt off. The 
weight of the residue taken from the 
weight left in the tared filter will 
give a very close approximation to the 
true amount of carbon used. The 
carbon in the residue may be deter- 
mined accurately by placing the 
dried carbon residue in a combustion 
furnace and running a regular car- 
bon combustion. This is seldom if 
ever necessarv. 



CHAPTER XX 
Physical Testing of Compounded Samples 



In addition to the chemical analysis 
it is necessary to make a number of 
physical tests of compounded samples. 

It is obvious in the beginning that 
not all the physical tests known 
should be carried out on every sam- 
ple submitted. For example, it is 
hardly necessary to test a solid tire 
for elasticity nor submit a toy bal- 
loon to an abrasion test. 

"We shall discuss the following 
tests and the reader will be able to 
judge where each will be used to 
advantage : 

1. Tensile strength 

2. Elongation 

3. Set 

4. Hardness 

5. Rebound 

6. Hysteresis 

7. Abrasion 

S. Penetration 
9. Tearing 

10. Specific Gravity 

11. Ageing Tests 

a. to heat 

b. to light 

c. to weather 

d. to artificial conditions 

12. Dielectric Power 

13. Viscosity 

14. Special Tests for pneumatic 

tires 

a. Friction test 

b. "Wearing tests on test cars 

c. Test tires 

15. Special tests for solid th'es 

a. Barbeque test 

b. Road tests 

No single one of the above tests is 
sufficient to recommend or to con- 
demn a sample, but several that are 
applicable must be tried and as a 
result of all these one arrives at a 
conclusion. 



Practically all of the above tests 
are to be carried out in a laboratory 
and therefore they are all more or 
less artificial. By this we mean that 
we are not subjecting the sample to 
the actual conditions under which 
the rubber will be used but we try 
to approach these conditions and 
from the results obtained speculate 
as to how that rubber will conduct 
itself under the conditions for which 
it was designed. 

Of course the most valuable test to 
which we can put any compound is 
to try it out where it is to be actu- 
ally used, but such tests consume too 
much time before results are avail- 
able. Then again the compounder 
wants to try out many new com- 
pounds, designing them for special 
purposes, and if it is possible to gain 
the information from some simple 
physical tests in the laboratory it 
saves both time and money. With 
this understanding we shall discuss 
the above physical tests. 

Tensile Strength 

The first in order is tensile strength 
and here we find several conditions 
which influence the results obtained. 
For instance, the kind of machine 
used ; the shape of the test pieces and 
how they are made; the speed at 
which the load is applied ; the tem- 
perature of the rubber when the test 
is being made ; and the grain of the 
rubber. 

There are several machines on the 
market each possessing certain merits. 
The ones in common use are the 
Scott. Olsen, Cooey. Schopper and 
Schwartz. Due to certain differences 
in these machines, and the peculiari- 
ties of rubber, it is difficult to obtain 
results which cheek well by using two 
different makes of machines. The 



132 



PHYSICAL TKSTING OF COMPOUNDED SAMPLES 



133 



Cooey runs a little more rapidly than 
the Olsen, and, as a matter of fact, 
the Cooey machine will show a greater 
tensile than the Olsen. Therefore it 




Fig. 40 — A Scott Rubbeb Tested 

is necessary when striving to obtain 
some comparative tests to use the 
same machine, whatever one that 
may be. 

The shape of the test piece and the 
way in which il is made is an im- 
portanl point in connection with 
tensile tests. 

The two forms most in use today 
are the straight pieces, which are 
enlarged at each end to allow the 
fixing of the clamps, and the ring 
form. The American machines use 
largely the straight pieces while the 
Schopper machine uses the ring form. 
These test strips are made either by 
cutting them out of a cured sheet by 
means of a die either with a press 
or by striking with a mallet. In 
some cases the sample is cured in a 



mold of the desired form for the test 
piece. This latter method is not as 
satisfactory as the use of a die, for 
it there remains a rind on the test 
piece after being removed from the 
mold, it must be trimmed off, and, 
in so doing, it is a very difficult mat- 
ter to avoid nicking the test piece 
itself; and if that is done the sam- 
ple will fall short of its correct ten- 
sile strength due to the tearing which 
will start from that point. 

In using the die, care must be taken 
to keep the cutting edges sharp and 
free from nicks. It will also be found 
that dipping it first into a basin con- 
taining a little water, just to moisten 
the cutting edges, will greatly aid in 
the work. 

In connection with the Schopper 
machine, there is a die press for cut- 
ting out the rings and also a caliper 
for determining the thickness of the 
sample. It is difficult to obtain the 
true thickness of the sample unless 
it is made from stock which has been 
calendered before curing, for other- 
wise it will vary some. The width is 




//^ 




Fig. 43 



governed by the die and is generally 
one-quarter of an inch as shown by 
the accompanying Fig. 41. 

Fig. 42 illustrates the ring test 
placed over the two pulleys of the 
Schopper machine ready to be tested. 
Fig. 43 represents the same ring after 



RUBBER MANUFACTURE 



the test is begun and the pulleys have 
moved apart a short distance and it 
will be observed that in such a test 
piece, the outer circumference of the 





Pig. 46 

. ring is stretched more than the inner 
circumference, or in other words it 
is under a greater strain than the 
inner and consequently the ring will 
fall short of its true tensile due to 
tearing. This is the greatest objec- 
tion to the ring form. 

The accompanying figures will 
illustrate the straight test pieces. 
Pig. 44 is termed the short one-half 
inch strip and is used with very 
elastic stocks which will not break 
in the range of the machine. Fig. 45 
is the one-fourth inch die and is used 
with stocks which have a high tensile. 
Fig. 46 is a short one-fourth inch die 
and is used with stocks possessing 
both a high tensile and a great elas- 
ticity. Ordinarily a test piece fails at 
its narrowest point and thus effects 
the break inside of the marks on the 
rubber. In ordinary work it has been 
stated by the Bureau of Standards 
that the small test pieces will give 
larger values than the larger strips, 
and in this connection the following 
data has been obtained. 

Die Used. Tensile. % Elongation. 

D % in 2440 470 

E % in 2S45 612 

F % in 2538 575 

From these figures the truth of 
that claim seems to be confirmed. 

To study the problem still further, 
sixty-four stocks were prepared and 
from each of these one 14-inch die. 
Fig. 45, was cut and one i/^-inch, 
Fig. 44, was taken. Then each strip 
was tested in the same machine. 
There jyere forty-nine instances 
where the 14-inch gave a tensile of 



100 pounds or more greater than the 
14-inch piece, thirty-three cases where 
the 14-inch piece proved that much 



Fig. 48 

the better, and forty-six cases where 
the two checked within 100 pounds. 
From this work it would seem that 
the differences in actual results are 
slight, whether the large or small 
strip is used. Considerable has been 
said concerning the speed with which 
the load is applied during a test. It 
has been known for some time that 
this point has a definite influence 
upon the tensile strength of a stock. 
That is the tensile strength indicated 
in a test depends to some extent upon 
the speed with which the rubber is 
stretched. 

And in Bulletin No. 38 of the 
Bureau of Standards the results of 
their experiments illustrate that 
point very clearly : 

No. 1 

Speed in in. per -mm 5 25 45 

Tensile strength per sq. in. 2405 2090 2720 

Elongation % 605 035 635 

No: 2 

Speed in in. per min o 25 45 

Tensile 1000 1940 1970 

Elongation 465 500 400 

No. 3 

Speed in in 5 25 45 

Tensile . 375 430 465 

Elongation 340 360 375 

From these figures, it is apparent 
that as the speed with which the load 
is applied is increased, the tensile 
strength will be higher. Of course 
there is a limit to this where increas- 
ing the speed will have no further 
effect upon the results. 

The average speed adopted for 
machines today . is from twenty to 
twenty-four inches per minute and 
this constant speed will always give 
comparative results, and that is what 
is desired. However, if check work 
is being done and different machines 
being used it would be advisable to 
take this factor into consideration. 

The temperature of the rubber 
when the test is being made also 



PHYSICAL TESTING OF COMPOUNDED SAMPLES 



135 



influences the results. Here again the 
Bureau of Standards has given some 
valuable experiments. Four stocks 
were made up and then test pieces 
taken, which were later tested at 
50° F., 70° F. and 90° F. Before each 
test was made, the room in which the 
work was done was maintained at the 
temperature desired for at least three 
hours. The exact results of these 
tests may be found in the Bulletin 
38 referred to above. 

First they found that the variation 
between 50° and 70° was much 
greater than between 70° and 90°, 
and as a result the Bureau now car- 
ries out these tests at 75° F. This 
is a temperature fortunately that is 
fairly easily maintained in working 
conditions. 

" Grain " 

When a sample of rubber is milled 
and perhaps calendered all in the 
same direction there results what 
may be termed " grain." Then if 




Pig. 49 — Olsen Vertical Testing 
Machine 

this sample is cured, the one cutting 
the test pieces has the choice of cut- 
ting them parallel with this grain or 
transverse to it. From considerable 



work done along this line it is plainly 
evident that the direction in Avhich 
the sample piece is cut does influence 
the results, therefore when obtaining 
comparison upon stocks, care must be 
taken in this particular. A theory by 
way of explanation of the phe- 
nomenon has been suggested by a 
friend and Fig. 47 illustrates the 
arrangement of rubber particles in a 
crude sample of rubber. The par- 
ticles may be considered as chains 
linked together as colloidal aggre- 
gates by fine threads similar to those 
obtained when a stirring rod is 
dipped into a glue gel and then is 
removed. As a result of the treat- 
ment through which the rubber has 
passed these chains are extending in 
all directions. Now during the mill- 
ing there is a tendency to straighten 
out these chains and thus bring them 
closer together as shown by Fig. 48. 

If the above theory has anything 
of truth in it, we should expect that 
a test strip cut longitudinally should 
contain more of the chains and thus 
give a larger tensile test than a strip 
ciit transversely or across the grain. 

To test this point the Bureau of 
Standards prepared four samples, 
taking both longitudinal and trans- 
verse test strips from each, and ob- 
tained the following results : 

Tensile strength 12 3 4 

Longitudinal 2730 2070 1200 880 

Transverse 2575 2030 1260 690 

% Elongation — 

Longitudinal 630 640 480 315 

Transverse 640 670 555 315 

Permanent Set after 300% elongation tor 
one minute with one minute rest. 

Longitudinal 11.2% 6% 22.1 % 34.3 

Transverse 7.3 5 16.3 25.0 

From these figures we see that the 
tensile strength is greater in the lon- 
gitudinal one, as would be expected. 
The permanent set runs higher in the 
longitudinal one also. 

Therefore we must take into con- 
sideration the above facts when carry- 
ing out tensile strength determina- 
tions. 

In addition to these points, a great 
deal of care and trouble is caused 
by the jaws which grip the test strips. 

As the rubber stretches its cross 
section grows less, therefore a jaw 
must be used which will tighten as 
the load is applied. 

The ring form of course obviates 



RUBBER MANUFACTURE 



these troubles for the rings pull 
around pulleys. 

One of the best forms of jaws is 
that used by the Olsen machine where 
eccentric disks grip the rubber and 
pull tighter as the rubber elongates. 

The weight shown by the machine 
should be indicated by a lever arm 
and not by a spring, as the latter re- 
quires calibrating too often. 

The actual determination of the 
tensile strength is then accomplished 
by pulling such a test strip whose 
exact thickness and width is known in 
one of the machines used above and 
then calculating and reporting the 
number of pounds which it requires to 
break a strip possessing a cross sec- 
tional area of one square inch. 

For example a test strip having 
a thickness of 11/64 of an inch and 
a width of % inch, sustained a pull of 
180 pounds before it failed. Its ten- 
sile strength is figured thus : 

1/2 times 11/64 = 11/128 square 
inches cross section area and this 
pulled 180 pounds, therefore its ten- 
sile strength will equal 1/11 of 180 = 
16.4 times 128 = 2029 pounds. The 
elongation test is generally carried 
out at the same time as the tensile 
strength test and on the same ma- 
chine. 

On the test piece, a distance of two 
inches is carefully marked off before 
placing it in the machine. As the 



load is applied, the distance between 
the two marks is carefully measured 
and when the sample fails the dis- 
tance is recorded in inches. The 
elongation is then figured as the per 
cent the original two inches is of the 
length it stretched before rupture. 
As an example the sample above 
elongated 11.3 inches, therefore its 
elongation is 11.3/2 times 100 — 
565%. The ring form machines are 
the only ones that possess an auto- 
matic device for recording the elon- 
gation and such an improvement will 
be welcomed for the other machines. 

The " set " or recovery is also 
determined at the same time as the 
above. The method used extensively 
has been to place the broken ends of 
the test strip together and measure 
the distance between the two marks 
which originally bound the two- 
inch distance before breaking. The 
measurement is made one minute 
after breaking and is referred to as 
immediate set in contrast to perma- 
nent set which is the more valuable. 
The set is also calculated in percent 
and represents the ratio of the stretch 
of the two inches to the total elon- 
gation. 

From the above example the two- 
inch marks were found to be 2.6 
inches apart after rupture and the 
elongation was 11.3 inches, therefore 



the immediate set is equal to 



11.3 



2.6 




Fig. 50 — Olsen's Autographic Rubber Testing Machine 



PHYSICAL TESTING OF COMPOUNDED SAMPLES 



times 100 or 5.3%. Several meth- 
ods have been tried and recommended 
for ascertaining permanent set. 
Beadle and Stevens suggest that the 
sample be stretched 400% and be 
held for twenty-four hours, then re- 
leased and measured six hours later. 
This will give comparable results if 
adhered to for general work, but re- 
quires too much time. 

In this as in immediate set there 
is the probability that in many speci- 
mens this will not give the true re- 
covery for there is likely to take 
place a tearing or breaking down of 
the rubber and this of course de- 
creases the set. Along this line the 
following experiment was tried: 

Half inch test pieces were prepared 
and then stretched 75% of the break- 
ing elongation. That is, if a sample 
elongated 13 inches it was stretched 
9.75 inches and held for one hour, 
two hours, three hours, eight hours, 
and sixteen hours. The set was meas- 
ured then in one minute, ten minutes, 
twenty minutes, forty minutes and 
sixty minutes and showed the fol- 
lowing : 

Time extended. 1M. 10M. 20M. 40M. 60M. 

1 in- 65 .49 .49 .46 .46 

2 In- 65 .63 .60 .50 .45 

3 lir 65 .55 .53 .52 .50 

S hr 68 .56 .54 .53 .52 

16 lir 75 .70 .67 .60 .53 

As a result of this experiment, the 
following method which is easily and 
rapidly carried out is to be recom- 
mended : 

The sample is stretched 60% of its 
elongation and held five minutes, then 
released and allowed to rest for three 
minutes. The sample is subjected to 
tins stress three times, then allowed 
to rest ten minutes and measurement 
made. By this shorter method about 
98% of the permanent set is found. 

Hardness 

Next in order of the physical tests 
is the property of ' ' Hardness. ' ' This 
is a property very difficult to define, 
which is possessed by all samples of 
rubber from the softest vulcanized 
rubber on one hand to the hardest 
vulcanite on the other. Various in- 
struments have been manufactured 
and sold for the purpose of determin- 
ing this property and yet no entirely 
satisfactory instrument is to be had at 



the present time. The general plan 
upon which these instruments have 
been constructed consists of a plunger 
of some sort with a point varying from 
a blunt needle up to a foot of quite 
measurable area. The measurement 
is taken of the depth this plunger will 
sink into the sample under a definite 
given load : Or what amounts to the 
same thing the measurement of the 
force necessary to cause the point of 
the plunger to sink into the rubber a 
definite depth. Under all circum- 
stances such an instrument should 
have a point sufficiently blunt that 
the surface of the sample shall not be 
ruptured during the test. 

These tests are the measure of the 
penetration by a blunt point without 
rupture of the rubber. The " re- 
bound " may be considered a test for 
resiliency. 

The instrument for this purpose 
consists of a metal tube with a slot 
along one side which is graduated 
from zero at the bottom to 100 at the 
top. A ball is placed in this tube in 
such a way that it may be allowed to 
fall freely through the tube its gradu- 
ated height when in a vertical posi- 
tion. The tube is put in place over 
the sample of rubber, which must be 
resting upon a firm base, in such a 
position that with the ball resting 
free on the sample it levels at zero on 
the scale. The ball is then raised 
until it occupies the same position 
with reference to the 100 mark. It is 
then released and the distance it re- 
bounds is carefully noted. This test 
is repeated as many times as seems 
desirable preferably at several dif- 
ferent points on the sample, then the 
average of these results is taken. 

This test is especially valuable on 
stocks used for cushioning. 

Hysteresis 

One phase of rubber testing which 
has received but comparatively little 
attention and that quite spasmodic, is 
the so called hysteresis test which 
really has to do with the contour of 
the curves representing the relation 
of the stress to elongation under the 
conditions of extension and recovery 
on not only the first but also on re- 
peated extensions. This includes: 



RUBBER MANUFACTURE 











ti 


_i 



Fig. 51 — A Plastometek 

1 — The detail of the contour of the re- 
spective curve. 

2 — The area under each respective 
curve which in turn represents 
the work required for extension, 
and the work done by the sample 
in retracting, the difference rep- 
resenting the work lost or hys- 
teresis loss. 

3 — The relation of the contours and 
areas represented by these differ- 
ent curves to each other. This of 
course includes the relation be- 
tween the percentage of elonga- 
tion produced by the same load 
under repeated flexing as well as 
the relation of the loads required 
to produce the same elongation. 
It also takes in the increase in set 
under repeated flexing. 

The reason for the lack of progress 
in this promising field becomes quite 
evident after an inspection of the 
necessary prerequisite of test speci- 



mens. These may be enumerated as 
follows : 

1 — The piece must be longitudinal 
and of uniform cross section 
throughout the entire length on 
which the graph is being recorded. 
2 — The several pieces which are being 
compared should be of the same 
cross section because of the diffi- 
culties in correcting for each of 
the infinite number of individual 
points on the curve for the differ- 
ence thus produced and the result- 
ing difference in the area produced 
underneath. 
3 — Xo portion of that section of the 
piece on which the record is being 
made can be subjected to the ac- 
tion of the jaws of the testing 
machine because of the numerous 
variations produced by cutting, 
tearing, slipping, etc. 
4 — Pieces with enlarged ends are en- 
tirely out of the question because 
of the great difference in percent- 
age of ultimate elongation pro- 
duced in various increments of 
the length of the piece under any 
increment of load. These differ- 
ences are so great as to completely 
obliterate those characteristics 
which are most sought. 
5 — King-shaped pieces are open to the 
same objection because of the 
great difference between the 
length represented by the inner 
and outer circumferences. 
The difference in cross section be- 
tween two pieces of the same shape 
may be either corrected, or. in case 
the cross sectional area is sufficiently 
large, the difference may become so 
small as to be negligible. 

Two methods of getting around the 
other difficulties have been suggested 
to the writer. The one is to follow 
two marks made on the narrow part 
of an ordinary longitudinal test piece 
with trammel points which are so con- 
nected with the recording device that 
only the actual increase in distance 
between the points is recorded. This 
device is a feature of the Tinius 
Olsen rubber testing machine. It is. 
however, practically impossible to 
produce a smooth curve with this de- 
vice. The other method is to attach 



PHYSICAL TESTING OF COMPOUNDED SAMPLES 



139 



clips similarly rigged, at the two 
marks on the piece. This scheme 
offers a chance for good development. 

Assuming that these points have 
been satisfactorily met, let us proceed 
to discuss the results to be obtained. 

Many men make much use of the 
relative general contour of the curves 
produced in the ordinary manner by 
the usual testing machines. They 
find themselves able to check their 
ideas on, cure, stiffness, etc., with 
much greater precision. Some make 
a. practice of accurately comparing 
several points on the curves. It 
would therefore seem highly desir- 
able to have an equation for the 
entire curve in which the various con- 
stants woidd present a ready and ac- 
curate means for such a comparison. 

M. Cheneveau and lleim have at- 
tempted such an equation (Stir I'ex- 
tensibilite du caoutchouc vulcanise 
Compt. rend. p. 320, Feb. 6. 1911, 
and in The Rubber Industry reports 
of the London convention in 1911). 
M. Cheneveau in Le Caoutchouc et la 
Gutta percha has later retracted his 
belief that the equation holds. B. L. 
Davies published a short article (Jour. 
I ltd. to Eng. Che in. VI., 985, 1914), 
with confirming experiments. In his 
lectures at the Municipal University 
of Akron, Mr. Davies has explained 
sonic further work along this line as 
follows : 

The equation does not seem to hold 
on the return curve or on the curve 
for successive cycles nor has he been 
able generally to apply the methods 



for obtaining the constants as ex- 
plained by Cheneveau and Heim. A 
much more simple and accurate 
method is presented through resort- 
ing to the principles of calculus. Fig. 
52 represents the ordinary type of 
curve : 

Assume that this curve is repre- 
sented by the Cheneveau and lleim 
equation : 

(1) x = ey-\-a sin' 2 by 

dx 

-?- — e-f2ab sin by cos by 

(2) =e+ah sin 2by 
x = 2ab cos 2by 



(4 



Now if we remember that 
dy _ 1 



= the slope 



dx e -^ ab sin 2 by 
of the tangent at any point we may 
draw the tangent and at any point 
find its slope and substitute in this 
equation. 

Then again bearing in mind that 
the second derivative is equal to zero 
at the point of inflexion, if we are 
able to estimate this point with fair 
accuracy to be at the point repre- 
sented by x y', we have 

(5) Cos 2by' = 

(6) or 2by' = r - 

whence b = -—. = ~ 
4*/ y' 

and from (4) since at y = or at 
y = 2y', sin 2 by = we have 



dy 1 

-j-=-= slop 
dx e 



of tic tangent at 



either of these points (this gives an- 
other proof of the correctness of tak- 
ing e as the inverse of the tangent -at 
the origin as suggested by Cheneveau 
and Heim). 

Again at the point of inflexion sin 

dy_ = _J 

dx e + a b 
= slope of the tangent at the point 
of inflection and froin (1) and '6; 



by' = 1 whence (8) 



x' = ey'-\-a sin 2 



Fig. 52 



= e y'+l\ 2 sin2 i) 



RUBBER MANUFACTURE 



= ey r + |( 1_cos i) 



= ey +- 

wherefore 

(9) a = 2 (x'-ey') 

We do not need any of this proof 
for a working basis, but have simply 
to remember that having located the 
point of inflection at x y we can 
draw the tangent at either the origin 
(where the curve is apt to be irregu- 
lar and therefore not ordinarily to be 
chosen) at the point of inflexion, or 
at the point where the ordinate of the 
point of inflexion and having drawn 
it determine its slope. The constants 
are then found from the following- 
simple equations: 

a = 2 (x' — ey') 

, r 45° 

o — -r~t or — r 

\y y 

e = the inverse of the slope of the 
tangent at the origin or at the point 
where the ordinate is twice the ordi- 
nate of the point of inflexion. 

Or e may be determined by equat- 
ing : — 7 to the slope of the inflexi- 

e + ab 

nal tangent. 

If we wish to find the area under 
the curve up to any point represented 
by x f y v we may integrate this equa- 
tion as follows : 

ry P 

Area O, (x p y p ), x v , 0=1 ey dy + 



1 



a sin 2 by dy 



Y 








| | | | | | | 




I.. 










Y= 0.65 X + 2.86 sin 2 9.1 X 








10 


























































8 


























































6 


























































4 


























































2 

























































































Vo 

ejfjr.ajU _ sin 2by v 
"2^2" 4b 



The chart here reproduced was 
drawn by means of clips attached at 
marks 2 in. apart on a test piece 
measuring 0.5 in. by 0.125 in. It was 
drawn on cross section paper ruled 
20 lines to the inch. Because the re- 
cording device reversed the curve on 
the chart, the equation becomes 

y = ex + a sin- b.v 

The unit of ordinate 0.5 in. repre- 
sents 34 per cent elongation; the unit 
of abscissa represents 167.5 lb. per 
sq. in. stress. One square inch there- 
fore represents 22.32 ft. lb. of work 
done. 

By taking the point of inflexion at 
r, = 4.95 and y, = 4.65 and using 
the foregoing equations. 
a = 2.86 

b = 9.10 deg. = 0.18 radians. 
e = 0.65 
and the equation y = ex + <7 sin- bx 
becomes 

y = 0.654a; + 2.86 sin 2 9.lx 

Comparing with actual figures we 
get 

In considering these results, it must 
be remembered that 0.05 in. on the 
chart represents 16.75 lb. on the x 



12.75 



335.0 
502.5 
670.0 



1S40.0 
2010.0 
2135.0 



Y computed. 
Ord. % Elong 



4.71 
5.S0 
6.S5 
7.S2 
S.66 
9.36 
9.92 
10.25 
11.85 



S7.2 
123.0 
161.0 
193.0 
234.0 
267.0 
296.0 
320.0 
339.0 
351.0 
405.0 



Y actual. 
Ord. % Elong 



9.S5 
10.35 
11.70 



316.0 
337.0 
353.0 
400.0 



2.0 
4.0 
3.0 
4.0 



11.2 
3.1 
2.4 
0.3 



PHYSICAL TESTING OF COMPOUNDED SAMPLES 



axis or oA per cent elongation; the 
maximum difference shown was, 
therefore, only about the width of the 
mark made by the tracing pen, and 
that the recording device was very 
crude. 

Integrating. 

?y = 0.653+2.86 sin 2 9.1a; 

-fa = 0.65 I xdx +2.86 



.65 j 



j 



12.75 

sin- 9.1 xdx 



0.65a:'- , 2.86.x 
2 



2.86 sin 18 .2a 

4 X .18 
= 69.06 
= 69.06 



r 



4 



17.26 sq. in. 



The area obtained by means of the 
planimeter on this area is not avail- 
able to the writer at present, but the 
two results differed by less than 0.1 
sq. in. 

The various relations between the 
areas of the various loops made by 
the initial and successive extensions 
and retractions should give a great 
deal of very desirable information es- 
pecially with regard to the resiliency 
of the stock and the rate of diminu- 
tion of the same. 

Beadle and Stevens have stated 
that the equation 

-~ L expresses the relation of the 

log n 

elongation produced by successive ex- 
tensions to the same stress. In this 
equation, 
L„ = Elongation at the end of the 

n th cycle 
i n = Elongation at the end of the 

first cycle 
log n = log of the number of cycles. 

The same relation may be obtained 
by plotting these results on logarith- 
mic cross section paper*, the result be- 
ing a straight line. The slope of this 
line is a measure of the cyclic fatigue. 

Instruments for measuring the 
abrasion of rubber have not as yet 
proved very successful. The general 



method is based on the principle of 
subjecting a weighed sample of rub- 
ber to the wearing action of a rotating 
wheel, having an emery or carborun- 
dum surface, either for a certain 
length of time or for a certain num- 
ber of revolutions. The sample is 
then reweighed and thus the weight 
of the rubber worn away is ascer- 
tained. For purposes of comparison 
it is generally reported in volume 
loss which is obtained by dividing the 
weight lost by the specific gravity of 
the stock. This test is of value with 
sole stocks as it gives a means of com- 
paring different compounds for wear- 
ing purposes. One of the difficulties 
to be overcome in this test is the man- 
ner in which the pressure of the rub- 
ber against the surface of the wheel 
is to be controlled and maintained 
constant. At present it is attempted 
to regulate the pressure by means of 
a dead weight or a lever. Although 
neither one is entirely satisfactory, 
yet if either is watched closely the 
conditions can be kept the same and 
therefore the results are comparable. 

A test for the purpose of learning 
something of the susceptibility of 
rubber to puncture is carried out on a 
machine for measuring the force nec- 
essary to puncture the stock. 

The instrument is similar to the 
one used for testing the hardness with 
the exception that the plunger carries 
a sharper point than the one used 
for gauging the hardness. The force 
necessary to cause the point to pene- 
trate the rubber is read directly from 
a dial graduated in arbitrary di- 
visions. 

No test with any degree of satis- 
faction has been devised for deter- 
mining the liability of a rubber to 
tear. 

Specific Gravity 

Specific gravity or density, in our 
use here may be regarded as the 
weight in air of the sample divided 
by the weight of an equal volume of 
water at 4 deg. C, the maximum den- 
sity of water. 

Several general methods are in use 
for this purpose but we shall outline 
only four, namely, hydrostatic, floata- 
tion, pycnometer and Jolly Balance. 



RUBBER MANUFACTURE 



By the hydrostatic method a sam- 
ple of any shape is taken, having a 
weight of not less than five grams 
and its weight in air ascertained. It 
is then suspended by means of a fine 
wire or horse hair and then dipped 
into water. Air bubbles are removed 
from the surface of the rubber by go- 
ing over it carefully with a camel's 
hair brush. This is necessary in all 
methods of determining density. A 
beaker of water is then placed on a 
support which straddles the pan of 
a balance. The piece of rubber is 
then suspended from the hook over 
the balance pan in such a manner that 
the rubber is immersed in the water 
when its exact weight is obtained. 
The weight of the horse hair im- 
mersed in the water must be obtained, 
then from the above procedure we 
have the weight of the rubber in air, 
plus the hair, minus the gross weight 
of the rubber and hair in water which 
will give the weight of the water dis- 
placed by the sample, or its volume. 
Since specific gravity equals weight 
divided by volume, we have the neces- 
sary data to obtain the density of the 



sample with reference to water at 
the temperature of the determina- 
tion. If it is desired to make the 
temperature correction, all that is 
necessary is to multiply the specific 
gravity so found by the density of the 
water at the temperature of the ex- 
periment. 

If it is desired to obtain the density 
of a sample lighter than water, it is 
necessary to use a sinker and its 
weight under water of course being 
known, the process is similar 1o the 
one given above. A piece of wire 
which is easily bent around the rub- 
ber serves this purpose very nicely. 

The floatation method is good for 
control work in the hands of inexperi- 
enced workmen as it requires no 
weighings. It is based upon the prin- 
ciple that solids having the same den- 
sity as liquids, when placed in them 
will neither rise nor sink and the 
density of the liquid is obtained by a 
hydrometer very easily. For samples 
with a gravity heavier than water, the 
density of the liquid is increased by 
the addition of solids which pass into 




Fig. 55 — Scott Model Q Horizontal Testing Machine 



PHYSICAL TESTING OF COMPOUNDED SAMPLES 



solution thus increasing the density. 
Zinc sulphate is used for such pur- 
poses. For instance, it is desired to 
produce a stock with a gravity of 1.42 
and continue this for some time. A 
zinc sulphate solution may be made 
up to the density and kept indefinitely 
provided that from time to time it is 
tested and corrected, for its density 
will increase due to evaporation. All 
that is necessary, therefore, to check 
up the stock is to cut off a piece of the 
material, sink it into the solution and 
note whether it sinks or rises. This 
is a rapid control method only. 

The pycnometer method is used 
largely for samples that exist as small 
pieces or powder, for they must be 
tested as powders. In some places the 
pycnometer is used altogether and the 
rubber to be tested is cut into narrow 
strips so that they will enter the bot- 
tle. This method is applicable to 
stocks either heavier or lighter than 
water. 

A pycnometer bottle is carefully 
cleaned, filled with the liquid in 
which the density is to be determined, 
and whose density is known and rep- 
resented by d. The filled pycnome- 
ter is then carefully weighed and this 
weight is represented by W. A cer- 
tain amount of the sample is then 
weighed and is represented by W x . 
This sample is then placed in the pyc- 
nometer and the bottle is carefully 
filled with the liquid and again 
weighed and the weight represented 
by W 3 . We now have the data neces- 
sary for the calculation of the spe- 
cific gravity of the sample. 

d equals density of liquid used. 

"Wj equals Wt. of sample in air. 

W„ equals Wt. of pycnometer and 
liquid. 

W, equals Wt. of pycnometer plus 
liquid plus sample. 

Therefore, the valume of water or 
liquid displaced is represented by 
Wj plus W„ minus W 3 , and since Sp. 

Wt. 
gr. equals ' we have Sp. gr. equals 



correction for water, then we must 
multiply the result so found by the 
density of the liquid at the tempera- 
ture of the experiment, or it may be 
included in the above formula and 
it would stand thus : Sp. gr. equals 

Wd 

W x plus Wo minus W 3 ' 

The Jolly Balance is a rapid 
method for the determination of the 
specific gravity and does not require 
the weighing of the sample on a deli- 
cate balance, thus making it possible 
for an inexperienced person to learn 
to carry on this test. 

The zero point on the balance must 
first be determined, then any shape 
or size of rubber is taken and placed 
in the upper pan of the balance with 
the lower pan immersed in water. 
The beaker of water is then raised 
and lowered until the disc comes to 
equilibrium in front of the line 
through the mirror. The stage is fast- 
ened in this position and the reading 
made on the graduated scale. The 
sample is then removed from the 
upper pan and placed on the lower 
one, which allows of the weighing of 
it under water. The point of equi- 
librium is again determined and the 
reading is made. The zero point 
taken from the first reading repre- 
sents its weight in air, W x ; the zero 
point taken from the second reading 
represents its weight in water, W, ; 
therefore, W x minus W 2 equals the 
water displaced and Sp. gr. equals 

W a 



-^r. Now if some 
Vv j plus W„ minus W 3 

liquid other than water were used or 
if we desire to make the temperature 



W t minus W., ' 

This may also be corrected for 
temperature by multiplying the re- 
sult thus obtained by the density of 
water at the temperature of the ex- 
periment. 

Specific gravity has been and is of 
great value in determining the use- 
fulness of a stock. Early in the in- 
dustry it was considered that the 
higher the density of a compound, the 
less its merit, for pure rubber has a 
gravity less than one, therefore, as 
gravity increased rubber must have 
decreased. This is true within certain 
limits and today with the different 
practices of the compounder, more 



RUBBER MANUFACTURE 



knowledge of a stock is necessary than 
simply its gravity. 

Artificial Ageing Tests 

The process of vulcanization in- 
creases the density of the stock and 
we, therefore, find that the specific 
gravity of cured rubber is always 
greater than that of the uncured 
dough. 

These are the methods in common- 
est use in the laboratories today. 

It is possible to learn a great deal 
from the results of ageing tests. As 
the term implies, the natural aging 
test requires a large amount of time 
before it is possible to obtain any 
results, therefore, artificial ageing 
tests have come into use. None of 
these artificial tests give all that is to 
be desired. 

The one in largest use today con- 
sists of heat treatment. It is known 
that vulcanization takes place at all 
temperatures, and that its rapidity 
depends upon the accelerators used 
and also the compound to some ex- 
tent. It follows then that if a sample 
is to be studied under certain condi- 
tions of elevated temperature the 
process of vulcanization is going to 
be continued. This will also vary 
with different stocks and thus com- 
parative results from which to draw 
our conclusions are difficult to obtain. 
At least there is the possibility of 
being seriously misled. 

Another point of difficulty arises 
from the fact that heat also tends to 
depolymerize the rubber. This is 
truer of some varieties than others; 
and is again a cause for a variance of 
results. 

We know that cured stocks tend to 
oxidize. An increase of temperature 
always favors this process, and it 
has been estimated that an increase of 
10 deg. C. will double the speed of 
the reaction, so it is perfectly clear 
that this influence must be taken into 
consideration. So we will mention 
two ageing tests that are studied 
under the inauence of heat. 

The first was proposed by Dr. Van 
Der Linde. He subjected the rubber 
to a temperature of 232 deg. F. for 
a period of two hours, thinking that 
in this time and at that temperature. 



the ultimate cure would be reached. 
Then by studying the physical prop- 
erties of the sample, such as its ten- 
dency to crack and its general appear- 
ance along with its tensile strength, 
set, and elongation as compared with 
a sample not subjected to the. treat- 
ment, he was able to draw his con- 
clusions. This has all of the objec- 
tions mentioned above and then the 
cracking is ouly reliable in stocks that 
have a . large amount of shoddy in 
them. The other heat treatment test 
was first used by Dr. G-eer. He blew 
air through an oven held at a tem- 
perature of 160 deg. P. When this 
•oven had become constant at work- 
ing conditions, several samples of rub- 
ber 3/32 of an inch in thickness were 
placed in it. Three samples were 
removed every day for a period of 
two weeks. These samples were then 
allowed to stand for twentj'-four 
hours until they had come to a state 
of equilibrium and were then tested 
for tensile strength and elongation. 
By this process the two sets of results 
were obtained and these were then 
plotted upon cross section paper. The 
curves thus obtained showed very 
clearly the time decay of the rubber. 
These were always compared against 
a standard stock which had been pre- 
viously determined. 

This test has the advantage over 
the other in that the temperature 
employed is much lower and thus the 
results of the criticisms mentioned 
above are reduced a great deal. Then, 
too, the possibility of interpreting 
the conclusion from a cure gives a 
better history of the stock. 

The cux'es obtained by this method 
have been studied in comparison with 
the ones obtained from natural ageing 
tests with the same stock, and a close 
agreement is always found. Such a 
test has even been found to be of 
great value for a stock that is used in 
places where part of its service con- 
sists in simply being stored, such as 
fire hose. 

Light Tests 

Again, rubber articles have been 
studied under the influence of light. 
It has been pointed out that certain 
light rays injure rubber and should, 
therefore, be a means of testing rub- 



PHYSICAL TESTING OF COMPOUNDED SAMPLES 



ber. No doubt the best test of this 
nature consists in subjecting the rub- 
ber to the direct action of the sun's 
rays. This enables one not only to 
study the effects upon the rubber but 
also to draw conclusions in regard to 
pigments used. This test, consumes 
too much time to be of any great 
value and it must always be carried 
out in conjunction with a standard 
sample. To shorten the time for this 
test, high power artificial lights have 
been tried but have not proved sat- 
isfactory. It is a difficult thing to 
imitate the white light given off by 
the sun. 

In carrying out the test the sam- 
ples must not be displayed behind 
glass which will cut off some of the 
rays whose effects it is so desirous to 
obtain. As a result of this it is dif- 
ficult to keep the temperature constant 
so that comparable results may be ob- 
tained at different seasons of the year. 
It is also known that drafts will in- 
fluence the results. It will be seen 
that a great many difficulties lie in 
the way of this test. 

Weather Exposure Tests 

Subjecting samples of rubber to ac- 
tual weather conditions is a very good 
test to establish one's opinion of a 
certain grade of stock. During the 
summer months especially, with fre- 
quent showers, and high temperature, 
a sample exposed to the weather un- 
dergoes about the severest test pos- 
sible. Then it is possible to obtain 
comparable results, for two samples 
may be exposed side by side and one 
of them be a standard against which 
the other is to be judged. The pres- 
ence of moisture in the air profound- 
ly influences this test just as has been 
observed many times in the rusting 
of iron, which is a process of oxida- 
tion. A dry piece of iron rusts very 
slowly if at all, while a moist one 
changes rapidly. So it is with rubber 
compounds. It may be claimed that 
the test is too slow but during the 
summer in two months' time the re- 
sults desired may be obtained. It is 
true that accidental compounds in 
the air may influence the results. For 
instance, if the samples are exposed 
to the weather in snch a place that 
they come in contact with consider- 



able sulphur dioxide, as it is thrown 
out of smokestacks, which, with the 
water in the air, forms sulphurous 
acid, thus in turn will oxidize to 
sulphuric acid and will produce its 
own effect upon the sample. 

This is a test, however, which it is 
good to use. 

To test rubber by artificial condi- 
tions we have in mind the carrying 
out of certain tests upon stocks, 
which, under the majority of circum- 
stances, they will not encounter in 
their life history and yet to which 
they may be subjected at certain 
times. 

For instance, it is well to see what 
effect certain road oils will have upon 
tread stocks as the tires may be used 
in a locality where the practice of oil- 
ing the roads is indulged in. Again, 
a machine standing in a garage may 
have its tires coming in contact with 
mineral oil and it is well to know 
what result such treatment will have 
upon the compound employed. In 
other words, it is a good practice to 
subject every stock, as far as prac- 
tical, to artificial conditions, of a 
chemical nature approaching the ac- 
tual conditions which the various ar- 
ticles will be subjected to in use. So 
the number of such tests is infinite 
and each workman should study his 
own problems and prepare and de- 
sign his own tests. 

Dielectric Tests 

A knowledge of the dielectric 
power of a stock is of value for those 
working with stocks employed in in- 
sulating wires and in making gloves 
for men handling high tension wires. 
For this purpose it is only necessary 
to determine the voltage that will 
break through a stock of certain 
thickness and this is always stated in 
the specifications. 

Viscosity Tests 

Viscosity determinations have been 
tried as a means of determining the 
degree of vulcanization of stocks, but 
have never proved to be of much 
value. It is a test which may be used, 
however, to cheek up and keep 
cements uniform. 

A very simple type of viscosimeter 
is obtained by taking a glass tube 



146 



RUBBER MANUFACTURE 



about one meter long with a diameter 
of ten centimeters. Place a cork in 
one end and then fill it with cement 
up to a certain mark. By means of 
a stop watch note how long it requires 
a shot to fall to the bottom. The time 
required compared with the time re- 
quired for it to fall through a simi- 
lar column of a standard cement gives 
the knowledge necessary to correct 
the one under consideration. 

Friction Tests 

In the making of pneumatic tires, 
the value of the finished product de- 
pends a great deal upon the friction 
employed. It is imperative, there- 
fore, that some test be made to learn 
the relative value of different fric- 
tions. 

The friction test is carried out on 
an ordinary tensile machine which is 
geared so that it is possible to run it 
at such a rate of speed that its jaws 
will separate two inches per minute. 
Then the machine must be equipped 
with jaws suitable to grip the fric- 
tion test piece. If it is desired to 
test the friction in a tire, a cross sec- 
tion of it is made just one inch wide 
or close to that and then its width 
carefully gauged. The first ply of 
the friction is then separated a lit- 
tle distance and fastened in the jaws 
of the test machine. The pull neces- 
sary to separate the ply is then re- 
corded on a chart and the pounds 
necessary to separate a strip one inch 
wide is calculated. A friction which 
requires twent3 r pounds pull to sepa- 
rate a ply one inch wide is regarded 
as satisfactory. 

Each ply in the tire is tested out by 
this procedure. 

When it comes, however, to test- 
ing the merits of one tire as com- 
pared with another, the most conclu- 
sive information is gained by put- 
ting them on a machine and run- 
ning until one fails and then noting 
the mileage covered. 

To get tests of value, they must be 



tried out in different parts of the 
country, thus obtaining different road 
conditions. Needless to say they 
should be used without chains. These 
actual service tests on what is known 
as test cars have been of great aid 
in perfecting the product of the tire 
industry of today. 

Barbeque Test 

When it comes to testing solid tires 
we have what is known as the Bar- 
beque test. This test if properly con- 
ducted is of great service for it aims 
to give us knowledge at the point 
most critical in a solid tire, namely, 
the strength of the union between the 
hard rubber base and the tire itself. 
To carry out this test, the tire is se- 
cured in a vise, and, by means of a 
knife, an oblique cut is made through 
the tire down to the hard rubber 
base. By means of pulling and using 
the knife also, a separation of a few 
inches is effected so that it is possible 
to pull up the tire proper and tie a 
rope around it. This rope is then 
tied to a scale capable of recording 
the pounds pull and the pulling begun 
at a tangent to the point of separa- 
tion. The number of pounds pull 
necessary to effect this separation of 
tire and base is carefully noted. The 
United States specifications require 
that for each inch of width at least 
100 pounds of pull will be required to 
separate it. 

This test has received severe criti- 
cism. 

Solid tires are also studied under 
test cars and in working conditions. 
The rate of wear on solid tires is 
measured by taking the height of 
the tire from time to time and study- 
ing it with reference to mileage. This 
is best done by plotting the rate of 
wear against mileage. 

It has not been our aim to even 
try to mention all the tests possible, 
but simply to give the reader an idea 
of how physical tests are studied and 
perhaps to suggest new lines of en- 
deavor in this field. 



APPENDIX 



The Laboratories and Equipment of the Municipal University 

of Akron 



Located in the center of the rubber 
manufacturing industry of the world, 
Buchtel College, now a part of the 
Municipal University of Akron, in 
file fall of 1908, installed among its 
courses the study of india-rubber and 
its use in industry. Dr. C. M. Knight, 
for thirty-eight years Professor of 
Chemistry in this institution, and to 
whom the present laboratory is dedi- 
cated, was the originator of the 
course. By virtue of his many years 
of teaching experience and his keen 
appreciation of the industrial de- 
mands of his city and country he had 
the wisdom to launch this work on 
a basis to insure success. He was 
of the firm belief that it was better 
to graduate a few men with a very 
high standard of ability than to turn 
out many with superficial knowledge. 

In erecting a fine building the foun- 
dation must first be laid with care ; 
so in securing an education that will 
permit of growth its foundation, 
too, must be deeply and carefully 
laid. 

In the University of Akron course 
one full year is first given to the 
study of inorganic chemistry. The 
student thus becomes familiar with 
the great laws under which the 
science operates. The second year 
he studies qualitative analysis. Con- 
trary to the requirements of a great 
many institutions, a full year of this 
work is required. A man has no 
license to be called a chemist until 
he is able to measure up as ah 
analyst. 

In the third year the student 
is mature enough, has technique 
enough, and is sufficiently grounded 
in principles to carry on quantita- 
tive analysis -and begin organic 



chemistry. In this year he covers 
simply the paraffin series of hydro- 
carbons. At the completion of this, 
the foundation is laid for the study of 
rubber chemistry, for, in addition to 
having had chemistry, he has also had 
German and French, mathematics 
and physics, as well as courses iu 
English and economics. The fourth 
year gives him the benzene series of 
hydrocarbons, rubber chemistry and 
advanced practical chemistry if he 
desires. 

The Rubber Laboratory Equipment 

The rubber laboratory is equipped 
to carry out all of the chemical ex- 
periments required in connection with 
the course. There is a rubber washer 
and mixing mill which is mounted 
on a large concrete base and driven 
by a motor. Another piece of ap- 
paratus is a steam generator with an 
automatic regulator. This furnishes 
the steam used in the press vulcan- 
izer, and also the kettle vulcanizer. 

A Tinius Olsen testing machine 
forms part of the equipment. 

With this outlay, it is possible to 
carry out actual work as the students 
will find it being done when they 
step into a factory laboratory. 

Brief Description of the Course 

Each subject naturally is composed 
of two parts: the lecture room work. 
consisting of lectures, quizzes, re- 
ports by students, etc., and the 
laboratory work. 

In the lecture room, the history of 
the crude rubber is given and then 
its development is traced into a great 
industry. The different species are 
studied with reference to source, col- 



147 



RUBBER MANUFACTURE 




The Knight Chemical Laboratory 



lection, coagulation, physical proper- 
ties and use. 

After some time is spent with the 
natural varieties, the plantation rub- 
bers are studied. Here it becomes 
necessary to emphasize some of the 
principles of colloidal chemistry, by 
which many of the phenomena of rub- 
ber are explained. 

After a discussion of the constitu- 
tion of rubber, the different possible 



methods of procuring the synthetic 
product are presented. Methods of 
carrying out both the chemical and 
physical testing of the crude rubber 
are then given. This work completes 
the first half of our year's work. 

The second half is devoted to the 
adapting of this india-rubber to the 
various articles of manufacture. 
Here theory is presented with the 
practical side as well. In connection 




One of the Laboratories 



with this lecture room work, there 
is running the parallel laboratory 
work. 

Beginning with the crude rubbers 
we study their peculiarities and their 







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De. C. M. Knight 

losses on being washed, likewise the 
action of different solvents on them. 
The fractional distillation of rubber 
is also interesting from a theoretical 
point of view at least. 

Thorough analyses along all the 
different lines of work are carried out 
here. We are of the opinion that a 
chemist first of all must be an analyst 



and capable of doing consistent work 
along this line. This is accomplished 
in the first half year, leaving the sec- 
ond to study compounding and physi- 
cal testing. 

It should be stated here that great 
value to our men is obtained from 
frequent visits to the large factories 
here. After studying the washing of 
rubber, and carrying it out in the 
laboratory, it is very helpful to visit, 
the wash rooms of two or more large 
concerns. This of course, applies to 
all divisions of the industry and, with 
the cooperation of the manufacturers 
of our city, we are able to study the 
various processes of manufacture in 
their factories. 

Two Industrial Fellowships 

Two industrial fellowships in tlie 
study of india-rubber have been 
established ; one by the Firestone Tire 
and Rubber Co., and the other by the 1 
Goodyear Tire and Rubber Co. 
These fellowships are awarded to the 
graduates of first grade chemical 
courses anywhere. The Fellow re- 
ceives three hundred dollars in money 
from the factory whose Fellowship he 
holds. At the end of a year he enters 
the employ of this company. The 
University gives him exemption from 
all fees but in return requires from 
him a maximum of twelve hours per 
week in way of laboratory supervision 
or correcting of note books or papers. 



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